Chapter 3: Chemical Industry Emissions 

2006 IPCC Guidelines for National Greenhouse Gas Inventories 3.1 

CHAPTER 3 

CHEMICAL INDUSTRY EMISSIONS 
Volume 3: Industrial Processes and Product Use 

3.2 2006 IPCC Guidelines for National Greenhouse Gas Inventories 

Authors 

Section 3.1 

Jochen Harnisch (Germany) 

Sections 3.2 – 3.8 

Charles Jubb (Australia) 

Alexander Nakhutin (Russia) and Virginia Carla Sena Cianci (Uruguay) 

Section 3.9 

Robert Lanza (USA) 

Thomas Martinsen (Norway), Abdul Karim W. Mohammad (Iraq), and Maruo M. O. Santos (Brazil) 

Section 3.10 

Archie McCulloch (UK) and Brian T. Mader (USA) 

Contributing Authors 

Sections 3.2 – 3.8 

Javier Pérez-Ramírez (Spain) 

Section 3.9 

Maarten Neelis (Netherlands) and Martin Patel (Germany) 
Chapter 3: Chemical Industry Emissions 

2006 IPCC Guidelines for National Greenhouse Gas Inventories 3.3 

Contents 

3 Chemical Industry Emissions......................................................................................................................3.10 

3.1 Introduction.........................................................................................................................................3.10 

3.2 Ammonia production...........................................................................................................................3.11 

3.2.1 Introduction .................................................................................................................................3.11 

3.2.2 Methodological issues .................................................................................................................3.11 

3.2.2.1 Choice of method...................................................................................................................3.12 

3.2.2.2 Choice of emission factors.....................................................................................................3.14 

3.2.2.3 Choice of activity data ...........................................................................................................3.15 

3.2.2.4 Completeness.........................................................................................................................3.17 

3.2.2.5 Developing a consistent time series.......................................................................................3.17 

3.2.3 Uncertainty assessment ...............................................................................................................3.17 

3.2.3.1 Emission factor uncertainties.................................................................................................3.17 

3.2.3.2 Activity data uncertainties .....................................................................................................3.17 

3.2.4 Quality Assurance/Quality Control (QA/QC), Reporting and Documentation ...........................3.17 

3.2.4.1 Quality Assurance/Quality Control........................................................................................3.17 

3.2.4.2 Reporting and Documentation ...............................................................................................3.18 

3.3 Nitric acid production..........................................................................................................................3.19 

3.3.1 Introduction .................................................................................................................................3.19 

3.3.2 Methodological issues .................................................................................................................3.19 

3.3.2.1 Choice of method...................................................................................................................3.20 

3.3.2.2 Choice of emission factors.....................................................................................................3.22 

3.3.2.3 Choice of activity data ...........................................................................................................3.23 

3.3.2.4 Completeness.........................................................................................................................3.24 

3.3.2.5 Developing a consistent time series.......................................................................................3.24 

3.3.3 Uncertainty assessment ...............................................................................................................3.24 

3.3.3.1 Emission factor uncertainties.................................................................................................3.24 

3.3.3.2 Activity data uncertainties .....................................................................................................3.25 

3.3.4 Quality Assurance/Quality Control (QA/QC), Reporting and Documentation ...........................3.25 

3.3.4.1 Quality Assurance/Quality Control........................................................................................3.25 

3.3.4.2 Reporting and Documentation ...............................................................................................3.25 

3.4 Adipic acid production ........................................................................................................................3.27 

3.4.1 Introduction .................................................................................................................................3.27 

3.4.2 Methodological issues .................................................................................................................3.27 

3.4.2.1 Choice of method...................................................................................................................3.27 

3.4.2.2 Choice of emission factors.....................................................................................................3.28 

3.4.2.3 Choice of activity data ...........................................................................................................3.30 

3.4.2.4 Completeness.........................................................................................................................3.31 
Volume 3: Industrial Processes and Product Use 

3.4 2006 IPCC Guidelines for National Greenhouse Gas Inventories 

3.4.2.5 Developing a consistent time series.......................................................................................3.31 

3.4.3 Uncertainty assessment ...............................................................................................................3.31 

3.4.3.1 Emission factor uncertainties.................................................................................................3.31 

3.4.3.2 Activity data uncertainties .....................................................................................................3.31 

3.4.4 Quality Assurance/Quality Control (QA/QC), Reporting and Documentation ...........................3.31 

3.4.4.1 Quality Assurance/Quality Control........................................................................................3.31 

3.4.4.2 Reporting and Documentation ...............................................................................................3.32 

3.5 Caprolactam, glyoxal and glyoxylic acid production..........................................................................3.33 

3.5.1 Introduction .................................................................................................................................3.33 

3.5.2 Caprolactam ................................................................................................................................3.33 

3.5.2.1 Methodological issues............................................................................................................3.33 

3.5.2.2 Uncertainty assessment..........................................................................................................3.37 

3.5.2.3 Quality Assurance/Quality Control (QA/QC), Reporting and Documentation......................3.38 

3.5.3 Glyoxal and glyoxylic acid production .......................................................................................3.39 

3.6 Carbide production..............................................................................................................................3.40 

3.6.1 Introduction .................................................................................................................................3.40 

3.6.2 Methodological issues .................................................................................................................3.40 

3.6.2.1 Choice of method...................................................................................................................3.41 

3.6.2.2 Choice of emission factors.....................................................................................................3.43 

3.6.2.3 Choice of activity data ...........................................................................................................3.44 

3.6.2.4 Completeness.........................................................................................................................3.45 

3.6.2.5 Developing a consistent time series.......................................................................................3.45 

3.6.3 Uncertainty assessment ...............................................................................................................3.45 

3.6.3.1 Emission factor uncertainties.................................................................................................3.45 

3.6.3.2 Activity data uncertainties .....................................................................................................3.45 

3.6.4 Quality Assurance/Quality Control (QA/QC), Reporting and Documentation ...........................3.46 

3.6.4.1 Quality Assurance/Quality Control........................................................................................3.46 

3.6.4.2 Reporting and Documentation ...............................................................................................3.46 

3.7 Titanium dioxide production...............................................................................................................3.47 

3.7.1 Introduction .................................................................................................................................3.47 

3.7.2 Methodological issues .................................................................................................................3.47 

3.7.2.1 Choice of method...................................................................................................................3.47 

3.7.2.2 Choice of emission factors.....................................................................................................3.48 

3.7.2.3 Choice of activity data ...........................................................................................................3.50 

3.7.2.4 Completeness.........................................................................................................................3.50 

3.7.2.5 Developing a consistent time series.......................................................................................3.50 

3.7.3 Uncertainty assessment ...............................................................................................................3.50 

3.7.3.1 Emission factor uncertainties.................................................................................................3.50 

3.7.3.2 Activity data uncertainties .....................................................................................................3.50 

3.7.4 Quality Assurance/Quality Control (QA/QC), Reporting and Documentation ...........................3.51 

3.7.4.1 Quality Assurance/Quality Control........................................................................................3.51 
Chapter 3: Chemical Industry Emissions 

2006 IPCC Guidelines for National Greenhouse Gas Inventories 3.5 

3.7.4.2 Reporting and Documentation ...............................................................................................3.51 

3.8 Soda ash production ............................................................................................................................3.52 

3.8.1 Introduction .................................................................................................................................3.52 

3.8.2 Natural soda ash production ........................................................................................................3.52 

3.8.2.1 Methodological issues............................................................................................................3.52 

3.8.2.2 Uncertainty assessment..........................................................................................................3.54 

3.8.2.3 Quality Assurance/Quality Control (QA/QC), Reporting and Documentation......................3.55 

3.8.3 Solvay soda ash production.........................................................................................................3.55 

3.8.3.1 Quality Assurance/Quality Control (QA/QC), Reporting and Documentation......................3.56 

3.9 Petrochemical and carbon black production........................................................................................3.57 

3.9.1 Introduction .................................................................................................................................3.57 

3.9.2 Methodological issues .................................................................................................................3.63 

3.9.2.1 Choice of method...................................................................................................................3.63 

3.9.2.2 Choice of emission factors.....................................................................................................3.72 

3.9.2.3 Choice of activity data ...........................................................................................................3.81 

3.9.2.4 Completeness.........................................................................................................................3.83 

3.9.2.5 Developing consistent time series..........................................................................................3.84 

3.9.3 Uncertainty assessment ...............................................................................................................3.84 

3.9.4 Quality Assessment/Quality Control (QA/QC), Reporting and Documentation.........................3.87 

3.9.4.1 Quality Assessment/Quality Control .....................................................................................3.87 

3.9.4.2 Reporting and Documentation ...............................................................................................3.88 

Annex 3.9A Feedstock-product flow diagrams ......................................................................................3.90 

3.10 Fluorochemical Production .................................................................................................................3.92 

3.10.1 HFC-23 emission from HCFC-22 production .............................................................................3.92

3.10.1.1 Introduction............................................................................................................................3.92 

3.10.1.2 Methodological issues............................................................................................................3.92 

3.10.1.3 Uncertainty assessment........................................................................................................3.100 

3.10.1.4 Quality Assurance/Quality Control (QA/QC), Reporting and Documentation....................3.101 

3.10.2 Emissions from production of other fluorinated compounds ....................................................3.102 

3.10.2.1 Introduction..........................................................................................................................3.102 

3.10.2.2 Methodological issues..........................................................................................................3.103 

3.10.2.3 Uncertainty assessment........................................................................................................3.106 

3.10.2.4 Quality Assurance/Quality Control (QA/QC), Reporting and Documentation....................3.106 

References.................................................................................................................................................... 3.107 
Volume 3: Industrial Processes and Product Use 

3.6 2006 IPCC Guidelines for National Greenhouse Gas Inventories 

Equations 

Equation 3.1 CO2 emissions from ammonia production – Tier 1 .............................................................3.12 

Equation 3.2 Total fuel requirement for ammonia production – Tier 2.....................................................3.13 

Equation 3.3 CO2 emissions from ammonia production – Tier 2 and 3....................................................3.13 

Equation 3.4 Total fuel requirement for ammonia production – Tier 3.....................................................3.13 

Equation 3.5 N2O emissions from nitric acid production – Tier 1............................................................3.21 

Equation 3.6 N2O emissions from nitric acid production – Tier 2............................................................3.21 

Equation 3.7 N2O emissions from adipic acid production – Tier 1...........................................................3.27 

Equation 3.8 N2O emissions from adipic acid production – Tier 2...........................................................3.28 

Equation 3.9 N2O emissions from caprolactam production – Tier 1.........................................................3.34 

Equation 3.10 N2O emissions from caprolactam production – Tier 2.........................................................3.35 

Equation 3.11 Emissions from carbide production.....................................................................................3.41 

Equation 3.12 CO2 emissions from titanium slag, synthetic rutile and rutile TiO2 production – Tier 1 .....3.48 

Equation 3.13 CO2 emissions from titanium slag, synthetic rutile and rutile TiO2 production – Tier 2 .....3.48 

Equation 3.14 CO2 emissions from natural soda ash production – Tier 1...................................................3.52 

Equation 3.15 Tier 1 CO2 emission calculation ..........................................................................................3.65 

Equation 3.16 Primary product production estimate calculation ................................................................3.65 

Equation 3.17 Overall Tier 2 mass balance equation..................................................................................3.67 

Equation 3.18 Estimate secondary product production from primary product [ethylene] production........3.67 

Equation 3.19 Estimate secondary product production from primary product [acrylonitrile] production ..3.67 

Equation 3.20 Tier 3 CO2 emissions calculation equation..........................................................................3.68 

Equation 3.21 Fuel combustion Tier 3 CO2 emissions calculation .............................................................3.68 

Equation 3.22 Flare gas Tier 3 CO2 emissions calculation .........................................................................3.69 

Equation 3.23 Tier 1 CH4 fugitive emission calculation.............................................................................3.70 

Equation 3.24 Tier 1 CH4 process vent emission calculation .....................................................................3.70 

Equation 3.25 Tier 1 CH4 total emissions calculation.................................................................................3.70 

Equation 3.26 Tier 3 CH4 emission calculation based on atmospheric measurement data.........................3.71 

Equation 3.27 Tier 3 CH4 emissions calculation equation..........................................................................3.71 

Equation 3.28 Fuel combustion Tier 3 CH4 emissions calculation .............................................................3.72 

Equation 3.29 Flare gas Tier 3 CH4 emissions calculation .........................................................................3.72 

Equation 3.30 Tier 1 calculation of HFC-23 from HCFC-22 (produced) using default factor ...................3.93 

Equation 3.31 Tier 2 calculation of HFC-23 from HCFC-22 (produced) using factor(s) calculated from 

process efficiencies..............................................................................................................3.93 

Equation 3.32 Calculation of HFC-23 emission factor from carbon balance efficiency.............................3.93 

Equation 3.33 Calculation of HFC-23 emission factor from fluorine balance efficiency...........................3.94 

Equation 3.34 Tier 3a calculation of HFC-23 emissions from individual process streams (direct method)......3.94 

Equation 3.35 Tier 3b calculation of HFC-23 emissions from individual process streams (proxy method) .....3.94 
Chapter 3: Chemical Industry Emissions 

2006 IPCC Guidelines for National Greenhouse Gas Inventories 3.7 

Equation 3.36 Tier 3c calculation of HFC-23 emissions from individual process streams (by monitoring 

reactor product) ...................................................................................................................3.95 

Equation 3.37 Tier 3a calculation of ‘instantaneous’ HFC-23 emissions in an individual process stream 

(direct method) ....................................................................................................................3.95 

Equation 3.38 Tier 3b calculation of HFC-23 emissions in an individual process stream (proxy method).......3.96 

Equation 3.39 Tier 3b calculation of standard emission for proxy method ................................................3.96 

Equation 3.40 Tier 3c calculation of HFC-23 emissions from an individual facility by in-process 

measurement........................................................................................................................3.97 

Equation 3.41 Tier 1 calculation of production-related emissions............................................................3.103 

Equation 3.42 Tier 3 direct calculation of production-related emissions..................................................3.104 

Equation 3.43 Tier 3 proxy calculation of production-related emissions..................................................3.104 

Figures 

Figure 3.1 Decision tree for estimation of CO2 emissions from ammonia production .........................3.14 

Figure 3.2 Decision tree for estimation of N2O emissions from nitric acid production........................3.22 

Figure 3.3 Decision tree for estimation of N2O emissions from adipic acid production.......................3.29 

Figure 3.4 Decision tree for estimation of N2O emissions from caprolactam, glyoxal or 

glyoxylic acid production ....................................................................................................3.36 

Figure 3.5 Decision tree for estimation of CO2 and CH4 emissions from carbide production..............3.43 

Figure 3.6 Decision tree for estimation of CO2 emissions from titanium dioxide production..............3.49 

Figure 3.7 Decision tree for estimation of CO2 emissions from natural soda ash production ..............3.53 

Figure 3.8 Decision tree for estimation of CO2 emissions from petrochemical industry and 

carbon black industry ..........................................................................................................3.63 

Figure 3.9 Decision tree for estimation of CH4 emissions from petrochemical industry and 

carbon black industry ..........................................................................................................3.64 

Figure 3.10 Tier 2 carbon mass balance flow diagram ...........................................................................3.66 

Figure 3.11 Methanol production feedstock-product flow diagram........................................................3.90 

Figure 3.12 Ethylene dichloride production feedstock-product flow diagram........................................3.90 

Figure 3.13 Ethylene oxide production feedstock-product flow diagram...............................................3.91 

Figure 3.14 Acrylonitrile production feedstock-product flow diagram ..................................................3.91 

Figure 3.15 Carbon black production feedstock-product flow diagram..................................................3.91 

Figure 3.16 Decision tree for HFC-23 emissions from HCFC-22 production 

(or other similar by-product emissions from fluorochemical production)...........................3.98 

Figure 3.17 Decision tree for emissions of fluorinated greenhouse gases from production processes, 

applicable to both fugitive and by-product emissions .......................................................3.105 
Volume 3: Industrial Processes and Product Use 

3.8 2006 IPCC Guidelines for National Greenhouse Gas Inventories 

Tables 

Table 3.1 Default total fuel requirements (fuel plus feedstock) and emission factors for ammonia 

production (per tonne NH3) .................................................................................................3.15 

Table 3.2 N2O abatement approaches and abatement measures..........................................................3.20 

Table 3.3 Default factors for nitric acid production ............................................................................3.23 

Table 3.4 Default factors for adipic acid production ...........................................................................3.30 

Table 3.5 Default factor for caprolactam production...........................................................................3.36 

Table 3.6 Default factors for glyoxal and glyoxylic acid production ..................................................3.39 

Table 3.7 Default factors for CO2 and CH4 emissions from silicon carbide production .....................3.44 

Table 3.8 Emission factors for CO2 emission from calcium carbide production and use....................3.44 

Table 3.9 Default factors for titanium dioxide production (tonnes CO2 per tonne product)................3.49 

Table 3.10 Specific carbon content of petrochemical feedstocks and products.....................................3.69 

Table 3.11 Petrochemical production Tier 1 default feedstocks and processes.....................................3.72 

Table 3.12 Methanol production CO2 emission factors.........................................................................3.73 

Table 3.13 Methanol production feedstock consumption factors..........................................................3.74 

Table 3.14 Steam cracking ethylene production Tier 1 CO2 emission factors.......................................3.75 

Table 3.15 Default Geographic Adjustment Factors for Tier 1 CO2 emission factors 

for steam cracking ethylene production...............................................................................3.75 

Table 3.16 Default methane emission factors for ethylene production .................................................3.76 

Table 3.17 Ethylene dichloride/vinyl chloride production process Tier 1 CO2 emission factors ..........3.77 

Table 3.18 Ethylene dichloride/vinyl chloride monomer process Tier 1 feedstock 

consumption factors.............................................................................................................3.77 

Table 3.19 Ethylene dichloride/vinyl chloride process Tier 1 default CH4 emission factor..................3.78 

Table 3.20 Ethylene oxide production feedstock consumption and CO2 emission factors....................3.78 

Table 3.21 Ethylene oxide production Tier 1 CH4 emission factors.....................................................3.79 

Table 3.22 Acrylonitrile production CO2 emission factors ...................................................................3.79 

Table 3.23 Carbon black production Tier 1 CO2 emission factors ........................................................3.80 

Table 3.24 Carbon black production Tier 1 CH4 emission factors ........................................................3.80 

Table 3.25 Ethylene steam cracking feedstock-product matrix.............................................................3.82 

Table 3.26 Secondary product production factors for acrylonitrile production process........................3.82 

Table 3.27 Uncertainty ranges for emission factors and activity data ...................................................3.86 

Table 3.28 HFC-23 default emission factors.........................................................................................3.99 
Chapter 3: Chemical Industry Emissions 

2006 IPCC Guidelines for National Greenhouse Gas Inventories 3.9 

Boxes 

Box 3.1 CO2 recovered for industrial gas..........................................................................................3.14 

Box 3.2 Double counting ..................................................................................................................3.16 

Box 3.3 Urea production...................................................................................................................3.16 

Box 3.4 Double counting ..................................................................................................................3.40 

Box 3.5 Allocation of emissions from CaO production....................................................................3.41 

Box 3.6 Double counting ..................................................................................................................3.48 

Box 3.7 Double counting ..................................................................................................................3.56 

Box 3.8 Methanol process descriptions.............................................................................................3.58 

Box 3.9 Ethylene process description ...............................................................................................3.59 

Box 3.10 Ethylene dichloride and vinyl chloride monomer process descriptions...............................3.59 

Box 3.11 Ethylene oxide process description .....................................................................................3.60 

Box 3.12 Acrylonitrile process description.........................................................................................3.61 

Box 3.13 Carbon black production process descriptions ....................................................................3.62 

Box 3.14 Plant measurement frequency............................................................................................3.100 
Volume 3: Industrial Processes and Product Use 

3.10 2006 IPCC Guidelines for National Greenhouse Gas Inventories 

3 CHEMICAL INDUSTRY EMISSIONS 

3.1 INTRODUCTION 

The following Sections 3.2 through 3.10 give guidance for estimating greenhouse gas emissions that result from 

the production of various inorganic and organic chemicals for which experience by a number of countries has 

confirmed significant contributions to global or individual national greenhouse gas emission levels. 

• Section 3.2 covers emissions from ammonia production; 

• Section 3.3 covers emissions from nitric acid production; 

• Section 3.4 covers emissions from adipic acid production; 

• Section 3.5 covers emissions from the production of caprolactam, glyoxal, and glyoxylic acid; 

• Section 3.6 covers emissions from the production of carbide; 

• Section 3.7 deals with emissions from the production of titanium dioxide; 

• Section 3.8 deals with emissions from the production of soda ash; 

• Section 3.9 covers emissions from key processes in the petrochemical and carbon black production, i.e., 

methanol, ethylene and propylene, ethylene dichloride, ethylene oxide, acrylonitrile, and carbon black; 

• Section 3.10 deals with emissions from fluorochemical production i.e., HFC-23 from the production of 

HCFC-22 and fugitive and by-product emissions from the production of other fluorinated compounds 

including hydrofluorocarbons (HFCs), sulphur hexafluoride (SF6) and uranium hexafluoride (UF6).

Care should be exercised to avoid double counting of carbon dioxide (CO2) emissions in both this chapter and in 

Volume 2 on Energy Sector, or, in omitting CO2 emissions since CO2 emissions resulting from carbon’s role as 

process reactant and as a heat source to drive the chemical reactions involved in the chemical processes can be 

closely related. Should CO2 capture technology be installed at a chemical plant, the CO2 captured should be 

deducted in a higher tier emissions calculation. Respective guidance on the capture and subsequent destruction 

or use of HFC-23 or other fluorochemicals is given in section 3.10. Any methodology taking into account CO2

capture should consider that CO2 emissions captured in the process may be both combustion and process-related. 

In cases where combustion and process emissions are to be reported separately, e.g., in the petrochemical 

industry, inventory compilers should ensure that the same quantities of CO2 are not double counted. In these 

cases the total amount of CO2 captured should preferably be reported in the corresponding energy combustion 

and IPPU categories in proportion to the amounts of CO2 generated in these source categories. The default 

assumption is that there is no CO2 capture and storage (CCS) taking place. For additional information on CO2

capture and storage refer to Volume 3, Section 1.2.2 and for more details to Volume 2, Section 2.3.4. 
Chapter 3: Chemical Industry Emissions 

2006 IPCC Guidelines for National Greenhouse Gas Inventories 3.11 

3.2 AMMONIA PRODUCTION 

3.2.1 Introduction 

Ammonia (NH3) is a major industrial chemical and the most important nitrogenous material produced. Ammonia 

gas is used directly as a fertiliser, in heat treating, paper pulping, nitric acid and nitrates manufacture, nitric acid 

ester and nitro compound manufacture, explosives of various types, and as a refrigerant. Amines, amides, and 

miscellaneous other organic compounds, such as urea, are made from ammonia (Austin, 1984; p.303). 

Ammonia production requires a source of nitrogen (N) and hydrogen (H). Nitrogen is obtained from air through 

liquid air distillation or an oxidative process where air is burnt and the residual nitrogen is recovered. Most 

ammonia is produced from natural gas (chiefly methane (CH4)), although H can be obtained from other 

hydrocarbons (coal (indirectly), oil), and water (Hocking, 1998; p.317). A small number of plants continue to use 

fuel oil as the fuel input and H source in the partial oxidation process. The carbon (C) content of the hydrocarbon 

is eliminated from the process at the primary steam reforming stage and shift conversion stage through 

conversion to carbon dioxide (CO2) which is the main potential direct greenhouse gas emission. Plants using 

hydrogen rather than natural gas to produce ammonia do not release CO2 from the synthesis process. 

3.2.2 Methodological issues 

The chemistry to obtain ammonia feedstocks is similar irrespective of the hydrocarbon used – CH4 or other fossil 

fuels (Hocking, 1998; p.319). Because the industry uses predominantly natural gas, the following outline of the 

process and sources of greenhouse emissions (CO2) is based on production using natural gas. Anhydrous 

ammonia produced by catalytic steam reforming of natural gas (mostly CH4) involves the following reactions 

with carbon dioxide produced as a by-product. 

Primary steam reforming: 

CH4 + H2O → CO + 3H2 

CO + H2O → CO2 + H2

Secondary air reforming: 

CH4 + air → CO + 2H2 + 2N2

Overall reaction: 

0.88CH4 + 1.26Air + 1.24H2O → 0.88CO2 + N2 + 3H2

Ammonia synthesis: 

N2 + 3H2 → 2NH3 

Secondary reformer process gas shift conversion: 

CO + H2O → CO2 + H2 

(Hocking, 1998; EFMA, 2000a; EIPPCB, 2004a) 

The processes that affect CO2 emissions associated with ammonia production are: 

• carbon monoxide shift at two temperatures using iron oxide, copper oxide and/or chromium oxide catalyst 

for conversion to carbon dioxide; 

• carbon dioxide absorption by a scrubber solution of hot potassium carbonate, monoethanolamine (MEA), 

Sulfinol (alkanol amine and tetrahydrothiophene dioxide) or others; 

• methanation of residual CO2 to methane with nickel catalysts to purify the synthesis gas. 

The production of ammonia represents a significant non-energy industrial source of CO2 emissions. The primary 

release of CO2 at plants using the natural gas catalytic steam reforming process occurs during regeneration of the 

CO2 scrubbing solution with lesser emissions resulting from condensate stripping. 

Should CO2 capture technology be installed and used at a plant, it is good practice to deduct the CO2 captured in 

a higher tier emissions calculation. The default assumption is that there is no CO2 capture and storage (CCS). In 

most cases, methodologies that account for CO2 capture should consider that CO2 emissions captured in the 

process may be both combustion and process-related. However, in the case of ammonia production no distinction 

is made between fuel and feedstock emissions with all emissions accounted for in the IPPU Sector. Similarly, all 

CO2 captured should be accounted for in the IPPU Sector. For additional information on CO2 capture and storage 

refer to Volume 3, Section 1.2.2 and for more details on capture and storage to Volume 2, Section 2.3.4. 
Volume 3: Industrial Processes and Product Use 

3.12 2006 IPCC Guidelines for National Greenhouse Gas Inventories 

CARBON DIOXIDE REGENERATOR 

After absorption of CO2 from the process gas, the saturated scrubbing solutions (e.g., potassium carbonate, MEA, 

etc.) are regenerated (i.e., for re-use) with steam stripping and/or boiling to release CO2 from the bicarbonates 

according to the following reactions: 

Heat 2KHCO3 → K2CO3 + H2O + CO2 

Heat (C2H5ONH2)2 + H2CO3 → 2C2H5ONH2 + H2O + CO2

The stripping gas, containing CO2 and other impurities, may be directed to a urea plant (where operational), to a 

liquid carbonic acid plant, or vented to the atmosphere (Environment Canada, 1987). 

CONDENSATE STRIPPER 

Cooling the synthesis gas after low temperature shift conversion forms a condensate containing small quantities 

of CO2 and other process impurities. The condensate is stripped by steam, whereby the components may be 

vented to the atmosphere, but normally recycled to the process together with the process stream (U.S. EPA, 

1985). 

3.2.2.1 CHOICE OF METHOD

The choice of method will depend on national circumstances as shown in the decision tree, Figure 3.1. Emissions 

are estimated from the total fuel requirement, or values derived from estimates of the total fuel requirement, used 

in the production of NH3. The fuel energy requirement is not accounted for separately. Note that values reported 

in energy units (or volume units) need to be converted to mass units when estimating emissions. 

Methods are classified according to the extent of plant-level data that are available. The Tier 1 method is based 

on default values and national statistics; the Tier 2 method is based on complete plant-level output data 

distinguished by fuel input type and process type, and default values; and the Tier 3 method is based entirely on 

plant-level input data. 

The Tier 3 method uses plant-level output data and plant-level fuel input per unit of output to derive the total fuel 

requirement. Similarly, Tier 3 can also use plant-level emission factors per unit of output provided that the 

source of these factors is plant-level detailed data on the fuel inputs per unit of output. 

TIER 1 METHOD 

The Tier 1 method uses ammonia production to derive emissions as follows: 

EQUATION 3.1 

CO2 EMISSIONS FROM AMMONIA PRODUCTION – TIER 1 

ECO2 AP FR CCF COF 44 12 − RCO2 = • • • •

Where: 

ECO2 = emissions of CO2, kg 

AP = ammonia production, tonnes 

FR = fuel requirement per unit of output, GJ/tonne ammonia produced 

CCF = carbon content factor of the fuel, kg C/GJ 

COF = carbon oxidation factor of the fuel, fraction 

RCO2 = CO2 recovered for downstream use (urea production), kg 

Ammonia production and emission factors can be obtained from national statistics and the emission factor can be 

determined from default values shown in Table 3.1. Where no information is available on the fuel type and/or 

process type, it is good practice to use the highest emission factor shown in Table 3.1. CO2 recovered for 

downstream use can be estimated from the quantity of urea produced where CO2 is estimated by multiplying 

urea production by 44/60, the stoichiometric ratio of CO2 to urea. When a deduction is made for CO2 used in 

urea production it is good practice to ensure that emissions from urea use are included elsewhere in the 

inventory. If data are not available on urea production it is good practice to assume that CO2 recovered is zero. 
Chapter 3: Chemical Industry Emissions 

2006 IPCC Guidelines for National Greenhouse Gas Inventories 3.13 

TIER 2 METHOD 

The initial step is to determine the total fuel requirement. For the Tier 2 method the total fuel requirement for 

each fuel type is estimated as follows: 

EQUATION 3.2 

TOTAL FUEL REQUIREMENT FOR AMMONIA PRODUCTION – TIER 2 

= ∑( • )

j

TFRi APij FRij

Where: 

TFRi = total fuel requirement for fuel type i, GJ 

APij = ammonia production using fuel type i in process type j, tonnes 

FRij = fuel requirement per unit of output for fuel type i in process type j, GJ/tonne ammonia produced 

Ammonia production, the fuel type and process type can be obtained from producers, and the fuel requirement 

per unit of output (FR) can be determined from the default values shown in Table 3.1. Emissions are derived 

according to Equation 3.3: 

EQUATION 3.3 

CO2 EMISSIONS FROM AMMONIA PRODUCTION – TIER 2 AND 3 

( ) 2 2 44 12 CO

i

ECO = ∑ TFRi •CCFi •COFi • − R

Where: 

ECO2 = emissions of CO2, kg 

TFRi = total fuel requirement for fuel type i, GJ 

CCFi = carbon content factor of the fuel type i, kg C/GJ 

COFi = carbon oxidation factor of the fuel type i, fraction 

RCO2 = CO2 recovered for downstream use (urea production, CO2 capture and storage (CCS)), kg 

When using the Tier 2 method, the C content of the fuel (CCF) and C oxidation factor (COF) may be obtained 

from the default values shown in Table 3.1 or country specific Energy Sector information. Data on CO2

recovered for urea production and CCS should be obtained from producers. 

TIER 3 METHOD 

The Tier 3 method requires that the fuel requirement be obtained from producers. The total fuel requirement is 

the sum of the total fuel requirements reported by each NH3 production plant. That is: 

EQUATION 3.4 

TOTAL FUEL REQUIREMENT FOR AMMONIA PRODUCTION – TIER 3 

= ∑

n

TFRi TFRin

Where: 

TFRi = total fuel requirement for fuel type i, GJ 

TFRin = total fuel requirement for fuel type i used by plant n, GJ 

Once data on total fuel requirements are collected and collated, CO2 emissions can be estimated using Equation 

3.3. When using the Tier 3 method, it is good practice to obtain information on the CCF and COF from 

producers or to use country specific energy sector information. As with the Tier 2 method, data on CO2

recovered for urea production (if any) and CCS (if undertaken) should be obtained from producers. 

Although data on ammonia production is not used in the calculation under the Tier 3 method it also needs to be 

collected from producers for reporting purposes. 
Volume 3: Industrial Processes and Product Use 

3.14 2006 IPCC Guidelines for National Greenhouse Gas Inventories 

BOX 3.1 

CO2 RECOVERED FOR INDUSTRIAL GAS

CO2 recovered for industrial gas applications is not accounted for separately as this is a relatively 

low volume short term use and it is assumed that all industrial gas carbon will be emitted to the 

atmosphere in the producing country. For example, industrial CO2 used in freezing applications is 

assumed to be released in the producing country. 

Figure 3.1 Decision tree for estimation of CO2 emissions from ammonia production 

Start

Are total

fuel input and CO2

recovered data available

directly from

plants?

Are national

aggregate ammonia 

production data

available?

Are ammonia

production data by fuel

type and process type 

available?

Yes

No

No

Collect data for the Tier 2

or Tier 3 method.

Use the plant-specific total fuel data

as basis for the Tier 3 method and 

subtract plant-specific CO2 recovered

for urea production and CO2 capture

and storage (CCS).

Calculate total fuel requirement by

fuel type, calculate emissions, and

subtract CO2 recovered for urea 

production and CO2 capture and 

storage (CCS).

Calculate emissions using

default emission factors and national 

aggregate ammonia production. 

Subtract CO2 recovered for urea 

production if data are available from

national statistics.

Box 1: Tier 1

Box 2: Tier 2

Box 3: Tier 3

Note:

1. See Volume 1 Chapter 4, Methodological Choice and Identification of Key Categories (noting Section 4.1.2 on limited resources), for 

discussion of key categories and use of decision trees.

Yes

No Is this a key

category1?

Gather production data or

use production capacity data.

Yes

No

Yes

3.2.2.2 CHOICE OF EMISSION FACTORS

TIER 1 METHOD 

If plant-level information is not available, it is good practice to use default factors. These default values often 

represent midpoint or mean values of data sets (as determined by expert analysis). The extent to which they 

represent a specific plant’s emission rate is unknown. Default factors by production process are provided in 

Table 3.1, and should be used only in cases where plant-specific data are not available. The default factors are 

estimates of total fuel requirements per unit of output expressed in energy units. They can be converted to mass 

units based on C content of the fuel and the C oxidation factor in Volume 2: Energy of these Guidelines. These 

values are also included in Table 3.1 as are emission factors of tonnes of CO2 per tonne of NH3 derived using 

these values. 
Chapter 3: Chemical Industry Emissions 

2006 IPCC Guidelines for National Greenhouse Gas Inventories 3.15 

For the Tier 1 method it is good practice to use the highest total fuel requirement per tonne of ammonia. If no 

information on fuel type is available, it is good practice to use the average value shown in Table 3.1 for partial 

oxidation. 

TABLE 3.1 

DEFAULT TOTAL FUEL REQUIREMENTS (FUEL PLUS FEEDSTOCK) AND EMISSION FACTORS FOR AMMONIA PRODUCTION 

(PER TONNE NH3) 

Production Process Total fuel requirement 

(GJ(NCV)/tonne NH3) 

± Uncertainty (%) 

Carbon content 

factor [CCF]1

(kg/GJ) 

Carbon oxidation 

factor [COF]1 

(fraction) 

CO2 emission 

factor 

(tonnes CO2 

/tonne NH3) 

Modern plants – Europe 

Conventional reforming – 

natural gas 

30.2 (± 6%) 15.3 1 1.694 

Excess air reforming – 

natural gas 29.7 (± 6%) 15.3 1 1.666 

Autothermal reforming – 

natural gas 30.2 (± 6%) 15.3 1 1.694 

Partial oxidation 

36.0 (± 6%) 21.0 1 2.772 

Derived from European 

average values for specific 

energy consumption (Mix of 

modern and older plants) 

Average value – natural gas 

37.5 (± 7%) 15.3 1 2.104 

Average value – 

partial oxidation 42.5 (± 7%) 21.0 1 3.273 

NCV – Net Calorific Value. 

1. Values from Energy, Vol. 2, Chapter.1, Tables 1.3 and 1.4.. 

Source: Adapted from EFMA (2000b; p.21); de Beer, Phylipsen and Bates (2001; p.21); for modern plants default factors can be derived 

using C content based on natural gas (dry basis) and partial oxidation default factors can be derived using C content based on residual 

fuel oil. 

TIER 2 METHOD 

The total fuel requirement values per unit of output in Table 3.1 can be used in conjunction with data on NH3

production by fuel type and process type, along with either default or country specific data on the C content 

factor and carbon oxidation factor of the fuels. 

TIER 3 METHOD 

Plant-level data on total fuel requirement provide the most rigorous data for calculating CO2 emissions from 

ammonia production. It is good practice to obtain information on the CCF and COF from producers or use 

country-specific Energy Sector data. The CCF is the key emission factor variable for deriving the quantity of 

CO2 emissions. Derivation of emissions using plant-level ammonia production depends on an accurate estimate 

of the fuel requirement per unit of output, along with information on the other variables. 

3.2.2.3 CHOICE OF ACTIVITY DATA

TIER 1 METHOD 

The Tier 1 method requires data on national production of NH3. If national-level activity data are not available, 

information on production capacity can be used. It is good practice to multiply the total national production 

capacity by a capacity utilisation factor of 80 percent ± 10 percent (i.e., a range of 70-90 percent) if the inventory 

compiler can document that utilisation for a year was below capacity. The same capacity utilisation factor should 

be applied to each year of the time-series. 

TIER 2 METHOD 

The Tier 2 method requires plant level data on ammonia production classified by fuel type and production 

process. In addition, plant level data on CO2 recovered for downstream use or other application are required. 
Volume 3: Industrial Processes and Product Use 

3.16 2006 IPCC Guidelines for National Greenhouse Gas Inventories 

TIER 3 METHOD 

The plant-level activity data required for the Tier 3 approach are total fuel requirement classified by fuel type, 

CO2 recovered for downstream use or other applications, ammonia production. Although ammonia production is 

not used in the Tier 3 calculation, collection of all activity data that influence the estimation of emissions allows 

changes over time and any misreporting of activity data to be identified. Where plant-level fuel requirement per 

unit of output is used, collection of plant-level production data is required. 

BOX 3.2 

DOUBLE COUNTING

In order to avoid double counting, the total quantities of oil or gas used (fuel plus feedstock) in 

ammonia production must be subtracted from the quantity reported under energy use in the 

Energy Sector. 

In addition, the quantity of CO2 recovered for downstream use in urea production must be 

subtracted from the total quantity of CO2 generated to derive CO2 emitted. Emissions of CO2 from 

urea use should be accounted for in the corresponding sectors. In particular, emissions from urea 

use as fertiliser should be included in the Agriculture Forestry and Other Land Use (AFOLU) 

Sector (see Volume 4). Emissions from urea use in automobile catalytic converters should be 

accounted for in the Energy Sector (Volume 2). Emissions from any other chemical products 

manufactured using CO2 recovered from the process (e.g., emissions from carbonic acid use) are 

covered by methodology suggested in this section and should not be accounted for in other IPPU 

sections or in other sectors. 

BOX 3.3 

UREA PRODUCTION

Urea (CO(NH2)2) (carbonyl amide or carbamide) is an important nitrogenous fertiliser with the 

highest nitrogen content available in a solid fertiliser. Urea is also used as a protein food 

supplement for ruminants, in melamine production, as an ingredient in the manufacture of resins, 

plastics, adhesives, coatings, textile anti-shrink agents, and ion-exchange resins (Austin, 1984; 

pp.311-312). A developing use is as a reducing agent in selective catalytic reduction of NOx in 

exhaust gases originating from diesel or gasoline direct injection engines. Emissions from urea 

applications should be accounted for in the appropriate application sectors. 

Urea production is a downstream process associated with ammonia production plants. The process 

uses the by-product CO2 stream from an ammonia synthesis plant along with ammonia. 

Urea is produced by the reaction of NH3 and CO2 to produce ammonium carbamate which is then 

dehydrated to urea according to the reactions: 

Ammonium carbamate production: 

2NH3 + CO2 → NH2COONH4

Dehydration of ammonium carbamate to urea: 

 NH2COONH4 → CO(NH2)2 + H2O 

Assuming complete conversion of NH3 and CO2 to urea, 0.733 tonnes of CO2 are required per 

tonne of urea produced. Greenhouse gas emissions from modern plants are likely to be small. 

Excess NH3 and CO2 are contained in the process water which is formed during the reaction. 

Water treatment is designed to recover these substances from the process water to enable recycling 

of the gases to the synthesis (EIPPCB, 2004a; p.118). Based on typical inputs for modern plants 

(EIPPCB, 2004a; p.121), the input values imply that emissions of CO2 range from 2 to 7kg per 

tonne of urea. For a plant of 1 000 tonnes of urea per day and assuming capacity utilisation of 

around 90 percent, this would imply annual emissions of CO2 of slightly in excess of 2Gg. 

Although emissions from urea production are unlikely to be significant in well-managed modern 

plants, it is good practice to obtain plant-level information on urea production and to account for 

any significant emissions. 
Chapter 3: Chemical Industry Emissions 

2006 IPCC Guidelines for National Greenhouse Gas Inventories 3.17 

3.2.2.4 COMPLETENESS

In countries where only a subset of plants report data for the Tier 3 method or where there is a transition from 

Tier 2 to Tier 3, it may not be possible to report emissions using Tier 3 for all facilities during the transition. 

Where data for the Tier 3 method are not available for all plants, Tier 2 could be used for the remaining plants. 

Also, where data for the Tier 2 method are reported by only a subset of plants or where there is a transition from 

Tier 1 to Tier 2, it may be possible to determine the share of production represented by non-reporting plants and 

use this information to estimate the remaining emissions using Tier 1 in order to ensure completeness during the 

transition period. 

Complete coverage for ammonia production requires accounting for all emissions from all sources. CO2

emissions are straightforward. Completeness can be improved by ensuring that emissions of any fugitive CH4

either from the primary reformer stage or catalytic methanation of CO2 process are included. In order to include 

emissions of NOx, CO and SO2 from the primary reformer stage, see guidance provided in Chapter 7 of Volume 

1: General Guidance and Reporting. 

3.2.2.5 DEVELOPING A CONSISTENT TIME SERIES

CO2 emissions should be recalculated for all years whenever emission calculation methods are changed (e.g., if 

the inventory compiler changes from the use of default values to actual values determined at the plant level). If 

plant-specific data are not available, including plant-specific production data and data for downstream use, for all 

years in the time series, it will be necessary to consider how current plant data can be used to recalculate 

emissions for previous years. It may be possible to apply current plant-specific emission factors to production 

data from previous years, provided that plant operations have not changed substantially. Recalculation is 

required to ensure that any changes in emissions trends are real and not an artefact of changes in procedure. It is 

good practice to recalculate the time series according to the guidance provided in Volume 1, Chapter 5. 

3.2.3 Uncertainty assessment 

3.2.3.1 EMISSION FACTOR UNCERTAINTIES

Uncertainties for the default values shown in Table 3.1 are estimates based on data from EFMA (2000a; p.21) 

and de Beer, Phylipsen and Bates (2001; p.21). In general, default emission factors for gaseous inputs and 

outputs have higher uncertainties than for solid or liquid inputs and outputs. Mass values for gaseous substances 

are influenced by temperature and pressure variations and gases are more easily lost through process leaks. It is 

good practice to obtain uncertainty estimates at the plant level, which should be lower than uncertainty values 

associated with default values. Default emission factor uncertainties reflect variations between plants across 

different locations. 

3.2.3.2 ACTIVITY DATA UNCERTAINTIES

Where activity data are obtained from plants, uncertainty estimates can be obtained from producers. These 

activity data are likely to be highly accurate (i.e., with uncertainty as low as ±2 percent). This will include 

uncertainty estimates for fuel use, uncertainty estimates for ammonia production and CO2 recovered. Data that 

are obtained from national statistical agencies usually do not include uncertainty estimates. It is good practice to 

consult with national statistical agencies to obtain information on any sampling errors. Where national statistical 

agencies collect data from the population of ammonia production facilities, uncertainties in national statistics are 

not expected to differ from uncertainties established from plant-level consultations. Where uncertainty values are 

not available from other sources, a default value of ±5 percent can be used. 

3.2.4 Quality Assurance/Quality Control (QA/QC), 

Reporting and Documentation 

3.2.4.1 QUALITY ASSURANCE/QUALITY CONTROL

It is good practice to conduct quality control checks as outlined in Volume 1, Chapter 6. More extensive quality 

control checks and quality assurance procedures are applicable, if higher tier methods are used to determine 
Volume 3: Industrial Processes and Product Use 

3.18 2006 IPCC Guidelines for National Greenhouse Gas Inventories 

emissions. Inventory compilers are encouraged to use higher tier QA/QC for key categories as identified in 

Volume 1, Chapter 4. 

Comparison of emission factors 

Inventory compilers should check if the estimated emission factors are within the range of default emission 

factors provided for the Tier 1 method, and also ensure that the emission factors are consistent with the values 

derived from analysis of the process chemistry. For example, the CO2 generation rate based on natural gas 

should not be less than 1.14 tonnes of CO2 per tonne of ammonia produced. If the emission factors are outside of 

the estimated ranges, it is good practice to assess and document the plant-specific conditions that account for the 

differences. 

Plant-specific data check 

The following plant-specific data are required for adequate auditing of emissions estimates: 

• Activity data comprising input and output data (input data should be total fuel requirement – fuel energy 

input plus feedstock input; 

• Calculations and estimation method; 

• List of assumptions; 

• Documentation of any plant-specific measurement method, and measurement results. 

If emission measurements from individual plants are collected, inventory compilers should ensure that the 

measurements were made according to recognised national or international standards. QC procedures in use at 

the site should be directly referenced and included in the QC plan. If the measurement practices were not 

consistent with QC standards, the inventory compiler should reconsider the use of these data. 

3.2.4.2 REPORTING AND DOCUMENTATION

It is good practice to document and archive all information required to produce the national emissions inventory 

estimates as outlined in Volume 1, Section 6.11. It is not practical to include all documentation in the national 

inventory report. However, the inventory should include summaries of methods used and references to source 

data such that the reported emissions estimates are transparent and steps in their calculation may be retraced. 

Much of the production and process data are considered proprietary by operators, especially where there are only 

a small number of plants within a country. It is good practice to apply appropriate techniques, including 

aggregation of data, to ensure protection of confidential data. Guidance on managing confidential data is 

provided in Section 2.2, Volume 1. 
Chapter 3: Chemical Industry Emissions 

2006 IPCC Guidelines for National Greenhouse Gas Inventories 3.19 

3.3 NITRIC ACID PRODUCTION 

3.3.1 Introduction 

Nitric acid is used as a raw material mainly in the manufacture of nitrogenous-based fertiliser. Nitric acid may 

also be used in the production of adipic acid and explosives (e.g., dynamite), for metal etching and in the 

processing of ferrous metals. 

During the production of nitric acid (HNO3), nitrous oxide (N2O) is generated as an unintended by-product of the 

high temperature catalytic oxidation of ammonia (NH3). The amount of N2O formed depends, inter alia, on 

combustion conditions (pressure, temperature), catalyst composition and age, and burner design (EFMA, 2000b; 

p.15). In addition, some NOx is produced. Formation of NOx is most pronounced at start-up and shut-down when 

the process is least stable (EFMA, 2000b; p.15). N2O is also generated in other industrial processes that use 

nitrogen oxides or nitric acid as feedstocks (e.g. the manufacture of caprolactam, glyoxal, and nuclear fuel 

reprocessing). Nitric acid is a significant source of atmospheric N2O if not abated and is the major source of N2O 

emissions in the chemical industry. While, unlike other emissions from nitric acid production, there are no 

mature technologies specifically designed for the destruction of N2O (Perez-Ramirez et al., 2003) a number of 

technologies for N2O mitigation during nitric acid manufacture have been developed in recent years. Examples 

include a tail-gas process where both N2O and NO emissions can be simultaneously reduced (requiring addition 

of ammonia to the tail-gas), a process-gas option involving direct catalytic decomposition right after the 

platinum gauzes, and a full-scale catalyst decomposition option. 

There are two types of nitric acid plants, single pressure plants and dual pressure plants. In single pressure plants 

the oxidation and absorption take place at essentially the same pressure, and in dual pressure plants absorption 

takes place at a higher pressure than the oxidation stage. 

3.3.2 Methodological issues 

Nitric acid production involves three distinct chemical reactions that can be summarised as follows: 

4NH3 + 5O2 → 4NO + 6H2O 

2NO + O2 → 2NO2

3NO2 + H2O → 2HNO3 + NO 

Nitrous oxide generation during the production of nitric acid is not well documented. Nitrogen oxidation steps 

under overall reducing conditions are considered to be potential sources of N2O. Nitric oxide (NO), an 

intermediate in the production of nitric acid, is also documented to readily decompose to N2O and nitrogen 

dioxide (NO2) at high pressures for a temperature range of 30 to 50oC (Cotton and Wilkinson, 1988). 

Perez-Ramirez et al. (2003; p.123) specify three intermediate reactions during the oxidation of ammonia that 

might result in the formation of N2O: 

NH3 + O2 → 0.5N2O + 1.5H2O 

NH3 + 4NO → 2.5N2O + 1.5H2O 

NH3 + NO + 0.75O2 → N2O + 1.5H2O 

Reactions that lead to the formation of N2O or N2 are undesirable in that they decrease the conversion efficiency 

of NH3 and reduce the yield of the desired product, NO (Perez-Ramirez et al., 2003; p.124). It is not possible to 

define a precise relationship between NH3 input and N2O formation because in general, ‘the amount of N2O 

formed depends on combustion conditions, catalyst composition and state (age), and burner design’ (PerezRamirez et al., 2003; p.123). Emissions of N2O depend on the amount generated in the production process and 

the amount destroyed in any subsequent abatement process. Abatement of N2O can be intentional, through 

installation of equipment designed to destroy N2O, or unintentional in systems designed to abate other emissions 

such as nitrogen oxides (NOx). 

Perez-Ramirez et al. (2003; p.126) classify abatement approaches as follows and abatement measures associated 

with each approach are outlined in Table 3.2: 
Volume 3: Industrial Processes and Product Use 

3.20 2006 IPCC Guidelines for National Greenhouse Gas Inventories 

• Primary abatement measures aim at preventing N2O being formed in the ammonia burner. This involves 

modification of the ammonia oxidation process and/or catalyst. 

• Secondary abatement measures remove N2O from the valuable intermediate stream, i.e. from the NOx gases 

between the ammonia converter and the absorption column. Usually this will mean intervening at the 

highest temperature, immediately downstream of the ammonia oxidation catalyst. 

• Tertiary abatement measures involve treating the tail-gas leaving the absorption column to destroy N2O. The 

most promising position for N2O abatement is upstream of the tail-gas expansion turbine. 

• Quaternary abatement measures are the pure end-of-pipe solution, where the tail-gas is treated downstream 

of the expander on its way to the stack. 

TABLE 3.2 

N2O ABATEMENT APPROACHES AND ABATEMENT MEASURES

Abatement approaches Abatement measures 

Primary abatement • Optimal oxidation process 

• Modification of platinum-rhodium gauzes 

• Oxide-based combustion catalysts 

Secondary abatement • Homogeneous decomposition in the burner 

• Catalytic decomposition in the burner (process gas 

catalytic decomposition) 

• Catalytic decomposition downstream of the burner 

(before the absorption column) 

Tertiary abatement • Thermal decomposition 

• Non-selective catalytic reduction (NSCR) 

• Tail-gas catalytic decomposition 

• Selective catalytic reduction (SCR) 

Quaternary abatement • Non-selective catalytic reduction (NSCR) 

• Catalytic decomposition 

• Selective catalytic reduction (SCR) 

Source: Adapted from Perez-Ramirez et al. (2003). 

The abatement achieved will depend on the technology implemented with tertiary measures stated as, ‘enabling 

the achievement of high levels of N2O removal (>99 percent)’ (Perez-Ramirez et al., 2003; p.136). Additionally, 

it is noted that although NSCR is a proven technology for N2O reduction, the replacement of NSCR systems by 

SCR systems for NOx reduction has a negative side-effect on its application for N2O reduction. Further, ‘NSCR 

is most likely not a viable option anymore, due to the high fuel consumption levels and high secondary 

emissions’ (Perez-Ramirez et al., 2003; p.137). 

Future adoption of technologies will depend on cost-effectiveness and the stringency of any emissions regulation. 

More cost-effective options are available for new plants than for existing plants. Tail-gas options are appealing 

since they do not interfere with the process. Direct N2O decomposition is a very attractive and cost effective 

option in plants with tail-gas temperatures greater than 723 K. However, two-thirds of the nitric acid plants in 

Europe have low-temperature tail-gases. To this end, preheating or using reductants (light hydrocarbons or 

ammonia) is required, making the after-treatment prohibitive. The most elegant and cost-effective option is the in 

process-gas catalytic decomposition, located in the heart of the plant (the ammonia burner). Concerns with this 

abatement option are chemical and mechanical stability of the catalyst as well as the possible NO loss. Several 

catalyst manufacturers and nitric acid producers have addressed this problem and catalysts are in the early stages 

of commercialisation. Advantageously, and contrary to the tail-gas option, this technology can be retrospectively 

applied to all existing plants. Further discussion of options is provided in Perez-Ramirez et al. (2003). 

3.3.2.1 CHOICE OF METHOD

The choice of good practice method depends on national circumstances. The decision tree in Figure 3.2 

describes good practice in adapting the methods to national circumstances. Emissions can be estimated from: 

• continuous emissions monitoring (CEM) where emissions are directly measured at all times; 
Chapter 3: Chemical Industry Emissions 

2006 IPCC Guidelines for National Greenhouse Gas Inventories 3.21 

• periodic emissions monitoring that is undertaken over a period(s) that is reflective of the usual pattern of 

operation of the plant to derive an emission factor that is multiplied by output (100 percent HNO3) to derive 

emissions; 

• irregular sampling to derive an emission factor that is multiplied by output (100 percent HNO3) to derive 

emissions; 

• by multiplying a default emission factor by output (100 percent HNO3). 

Methods are classified according to the extent of plant-level data that are available. Both Tier 2 and Tier 3 are 

based on plant-level activity data. 

TIER 1 METHOD 

Emissions are estimated as follows: 

EQUATION 3.5 

N2O EMISSIONS FROM NITRIC ACID PRODUCTION – TIER 1 

EN2O = EF • NAP

Where: 

EN2O = N2O emissions, kg 

EF = N2O emission factor (default), kg N2O/tonne nitric acid produced 

NAP = nitric acid production, tonnes 

When applying the Tier 1 method it is good practice to assume that there is no abatement of N2O emissions and 

to use the highest default emission factor based on technology type shown in Table 3.3. 

TIER 2 METHOD 

There are a large number of nitric acid plants (estimates range from 255 to 600 plants according to Choe et al., 

1993; Bockman and Granli, 1994) with substantial variations in the N2O generation factors among plant types. 

Consequently, default factors may be needed more often for nitric acid N2O emissions estimates. Where default 

values are used to estimate emissions from nitric acid production, it is good practice to categorise plants 

according to type and to use an appropriate N2O generation factor. 

The Tier 2 method uses plant-level production data disaggregated by technology type and default emission 

factors classified by technology type. Emissions are calculated as follows: 

EQUATION 3.6 

N2O EMISSIONS FROM NITRIC ACID PRODUCTION – TIER 2

= ∑[ • • ( ) − • ]

i j

EN O EFi NAPi DFj ASUFj , 2 1

Where: 

EN2O = emissions of N2O, kg 

EFi = N2O emission factor for technology type i, kg N2O/tonne nitric acid produced 

NAPi = nitric acid production from technology type i, tonnes 

DFj = destruction factor for abatement technology type j, fraction 

ASUFj = abatement system utilisation factor for abatement technology type j, fraction 

Note that the default emission factors shown in Table 3.3 include the impact on emissions of abatement 

technology where relevant. To use these factors, inventory compilers should verify that the abatement 

technology is installed at individual plants and operated throughout the year. 

The basic equation for estimating N2O emissions includes additional terms that recognise the potential future use 

of N2O abatement technologies. The N2O destruction factor has to be multiplied by an abatement system 

utilisation factor in order to account for any down-time of the emission abatement equipment (i.e., time the 

equipment is not operating). 
Volume 3: Industrial Processes and Product Use 

3.22 2006 IPCC Guidelines for National Greenhouse Gas Inventories 

TIER 3 METHOD – DIRECT MEASUREMENT 

While the tier 2 approach applies technology specific emission factors reflecting the national technology mix. 

Tier 3 is based on real measurement data (e.g., CEMS). Plant-level production data disaggregated by technology 

type and plant level emission factors obtained from direct measurement of emissions. These may be derived 

from irregular sampling of emissions of N2O or periodic emissions monitoring of N2O undertaken over a 

period(s) that reflects the usual pattern of operation of the plant. Emissions can be derived using Equation 3.6. 

Alternatively, the Tier 3 method uses the results of continuous emissions monitoring (CEM), although it is noted 

that most plants are unlikely to employ CEM due to the resource costs. Where CEM is employed, emissions can 

be estimated based on the sum of measured N2O emissions derived from the concentration of N2O in monitored 

emissions for each recorded monitoring interval. 

Figure 3.2 Decision tree for estimation of N2O emissions from nitric acid production 

Start

Are direct

measurement data

available?

Is this a key

category1

?

Are

plant-specific

activity data on nitric acid

production

available?

Yes

No

No

Collect data for the Tier 3

or Tier 2 method.

Use plant specific-emissions data

and activity data (irregular sampling

data, periodic monitoring data or 

continuous emissions monitoring) as 

basis for Tier 3 method.

Use plant-specific data on quantity

of nitric acid by technology type 

produced as basis for Tier 2 method.

Use national data on nitric acid 

production or national data on

capacity, and default emission factors.

Box 1: Tier 1

Box 2: Tier 2

Box 3: Tier 3

Note:

1. See Volume 1 Chapter 4, Methodological Choice and Identification of Key Categories (noting Section 4.1.2 on limited resources), for 

discussion of key categories and use of decision trees.

Yes

No

Yes

3.3.2.2 CHOICE OF EMISSION FACTORS

TIER 1 METHOD 

It is good practice to use the highest emission factor based on the technology type shown in Table 3.3 and to 

assume that there is no abatement of N2O emissions. 

TIER 2 METHOD 

If plant-level factors are not available, it is good practice to use default factors. These default values often 

represent midpoint or mean values of data sets (as determined by expert analysis). The extent to which they 
Chapter 3: Chemical Industry Emissions 

2006 IPCC Guidelines for National Greenhouse Gas Inventories 3.23 

represent a specific plant’s emission rate is unknown. Default factors in Table 3.3 should be used only in cases 

where plant-specific measurements are not available. 

Table 3.3 includes emission factors for N2O, and associated uncertainties. The factors listed in Table 3.3 for 

plants using non-selective catalytic reduction (NSCR), (a NOx abatement technology that can also be managed to 

abate N2O), already incorporate the effect of N2O abatement measures. To use these factors, inventory compilers 

should verify that the abatement technology is installed at individual plants and operated throughout the year. 

TIER 3 METHOD 

Plant measurements provide the most rigorous data for calculating net emissions (i.e., N2O generation and 

destruction factors). Monitoring N2O emissions from nitric acid production is practical because these are point 

sources and there are a finite number of production plants. Given currently available technology, instrumentation 

for sampling and monitoring emission rates do not limit precision or accuracy of the overall measurement. 

Usually sampling frequency and timing is sufficient to avoid systematic errors and to achieve the desired level of 

accuracy. 

As a general rule, it is good practice to conduct sampling and analysis whenever a plant makes any significant 

process changes that would affect the generation rate of N2O, and sufficiently often otherwise to ensure that 

operating conditions are constant. In addition, plant operators should be consulted annually to determine the 

specific destruction technologies employed and confirm their use, since technologies may change over time. 

Precise measurement of the emissions rate and abatement efficiencies requires measurement of both the exit 

stream and the uncontrolled stream. Where measurement data are available only on the exit stream, good 

practice is to base emissions on these data. In this case, any available estimates of abatement efficiency should 

be provided only for information purposes and are not used to calculate emissions. 

TABLE 3.3 

DEFAULT FACTORS FOR NITRIC ACID PRODUCTION

Production Process N2O Emission Factor 

(relating to 100 percent pure acid) 

Plants with NSCRa (all processes) 2 kg N2O/tonne nitric acid ±10% 

Plants with process-integrated or tailgas N2O destruction 2.5 kg N2O/tonne nitric acid ±10% 

Atmospheric pressure plants (low pressure) 5 kg N2O/tonne nitric acid ±10% 

Medium pressure combustion plants 7 kg N2O/tonne nitric acid ±20% 

High pressure plants 9 kg N2O/tonne nitric acid ±40% 

a Non-Selective Catalytic Reduction (NSCR). 

Source: van Balken (2005). 

3.3.2.3 CHOICE OF ACTIVITY DATA

It is good practice to compile production data at a level of detail that allows the use of a Tier 2 or Tier 3 method, 

where possible. Activity data should be based on 100 percent HNO3, - it is good practice to ensure that all 

production data reported are for 100 percent HNO3. 

TIER 1 METHOD 

The Tier 1 method requires data on national production of nitric acid. National nitric acid statistics may omit a 

substantial proportion of the national total (see details in Section 3.3.2.4 Completeness). If national-level activity 

data are not available, information on production capacity can be used. It is good practice to multiply the total 

national production capacity by a capacity utilisation factor of 80 percent ± 10 percent (i.e., a range of 70-90 

percent). 

TIER 2 METHOD 

The Tier 2 method requires plant-level production data disaggregated by technology type and abatement system 

type. It is good practice to gather activity (production) data at a level of detail consistent with that of any 

generation and destruction data. Typical plant-level production data is assumed to have an uncertainty of ±2 

percent due to the economic value of having accurate information. 
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3.24 2006 IPCC Guidelines for National Greenhouse Gas Inventories 

TIER 3 METHOD 

As with the Tier 2 method, plant-level production data disaggregated by technology and abatement system type 

are required. It is good practice to gather activity (production) data at a level of detail consistent with that of any 

generation and destruction data. Although production data are not used in the estimation of emissions where the 

estimate is based on CEM, these data should be collected and reported to ensure that changes in variables that 

influence emissions can be monitored over time. Typical plant-level production data is assumed to have an 

uncertainty of ±2 percent due to the economic value of having accurate information. 

3.3.2.4 COMPLETENESS

Nationally compiled nitric acid production statistics could underestimate production. Studies that compare global 

statistics compiled from national data on nitric acid production with industry estimates of global production 

suggest that the national statistics account for only 50 to 70 percent of the total (Bouwman et al., 1995; Olivier, 

1999). This is probably due to nitric acid production that is integrated as part of larger production processes, 

where the nitric acid never enters into commerce and is not counted in the national statistics. It is good practice

to account for these sources by methods such as identifying them through national registries of NOx emissions, 

another unintended by-product of nitric acid production. 

NSCR and SCR systems designed to abate N2O can give rise to additional emissions of CO, CO2 and 

hydrocarbons (CH4 and NMVOCs). These emissions will depend on the hydrocarbon reducing agent that is used 

(methane (CH4), propane (C3H8), propene (C3H6), LPG). Emissions can be estimated based on the quantity of 

reducing agent used and the completeness of combustion. Plant-level information will be required to enable 

emissions estimation. Over time default values could be developed as more information becomes available, 

however, at present there are no default values. Methods for estimating these emissions are not included in these 

Guidelines, however, inventory compilers are encouraged to investigate these emission sources and to develop 

appropriate methodologies. 

There will usually be few nitric acid plants in a country, and it is suggested that emissions are calculated from 

plant specific data. In countries where only a subset of plants report data for the Tier 3 method or where there is 

a transition from Tier 2 to Tier 3, it may not be possible to report emissions using Tier 3 for all facilities during 

the transition. Where data for the Tier 3 method are not available for all plants, Tier 2 could be used for the 

remaining plants. Also, where data for the Tier 2 method are reported by only a subset of plants or where there is 

a transition from Tier 1 to Tier 2, it may be possible to determine the share of production represented by nonreporting plants and use this information to estimate the remaining emissions using Tier 1 in order to ensure 

completeness during the transition period. 

3.3.2.5 DEVELOPING A CONSISTENT TIME SERIES

N2O emissions should be recalculated for all years whenever emission calculation methods are changed (e.g., if 

the inventory compiler changes from the use of default values to actual values determined at the plant level). If 

plant-specific data are not available for all years in the time series, it will be necessary to consider how current 

plant measurements can be used to recalculate emissions for previous years. It may be possible to apply current 

plant-specific emission factors to production data from previous years, provided that plant operations have not 

changed substantially. Such a recalculation is required to ensure that any changes in emissions trends are real 

and not an artefact of changes in procedure. It is good practice to recalculate the time series according to the 

guidance provided in Volume 1, Chapter 5. 

3.3.3 Uncertainty assessment 

3.3.3.1 EMISSION FACTOR UNCERTAINTIES

Uncertainties for the default values shown in Table 3.3 are estimates based on expert judgment. In general, 

default emission factors for gaseous substances have higher uncertainties because mass values for gaseous 

substances are influenced by temperature and pressure variations and gases are more easily lost through process 

leaks. The default values for nitric acid production have a relatively high level of uncertainty for two reasons. 

First, N2O may be generated in the gauze reactor section of nitric acid production as an unintended reaction byproduct (Cook, 1999). Second, the exhaust gas may or may not be treated for NOx control, and the NOx
Chapter 3: Chemical Industry Emissions 

2006 IPCC Guidelines for National Greenhouse Gas Inventories 3.25 

abatement system may or may not reduce (or may even increase) the N2O concentration of the treated gas1. It is 

good practice to obtain uncertainty estimates at the plant-level which should be lower than uncertainty values 

associated with default values. 

3.3.3.2 ACTIVITY DATA UNCERTAINTIES

Where activity data are obtained from plants, uncertainty estimates can be obtained from producers. Data that are 

obtained from national statistical agencies usually do not include uncertainty estimates. It is good practice to 

consult with national statistical agencies to obtain information on any sampling errors. Where national statistical 

agencies collect data from the population of nitric acid production facilities, uncertainties in national statistics 

are not expected to differ from uncertainties established from plant-level consultations. Where uncertainty values 

are not available from other sources, a default value of ±2 percent can be used. To reduce uncertainty it is good 

practice to ensure that all activity data are for 100 percent HNO3. 

3.3.4 Quality Assurance/Quality Control (QA/QC), 

Reporting and Documentation 

3.3.4.1 QUALITY ASSURANCE/QUALITY CONTROL

It is good practice to conduct quality control checks as outlined in Volume 1, Chapter 6. More extensive quality 

control checks and quality assurance procedures are applicable if higher tier methods are used to determine 

emissions. Inventory compilers are encouraged to use higher tier QA/QC for key categories as identified in 

Volume 1, Chapter 4. 

Comparison of emissions estimates using different approaches 

If emissions are calculated using data from individual nitric acid plants (bottom-up approach), inventory 

compilers should compare the estimate to emissions calculated using national production data (top-down 

approach). They should record the results and investigate any unexplained discrepancies. 

Since industrial N2O source categories are relatively small compared to other anthropogenic and natural sources, 

it is not feasible to compare emissions with measured trends in atmospheric N2O concentrations. 

Plant-level data 

Inventory compilers should archive sufficient information to allow an independent review of the time series of 

emissions beginning in the base year, and to explain trends in emissions when making historical comparisons. 

This is particularly important in cases where recalculations are necessary, for example, when an inventory 

compiler changes from using default values to actual values determined at the plant level. 

Revision of direct emission measurements 

If plant-level N2O measurements are available, inventory compilers should confirm that internationally 

recognised, standard methods were used. If the measurement practices fail this criterion, then they should 

evaluate the use of these emissions data. In addition, they should reconsider the uncertainty estimates in light of 

the QA/QC results. 

Inventory compilers should compare plant-based factors to the IPCC defaults to ensure that the plant-specific 

factors are reasonable. They should explain and document any differences between plant-specific factors and 

default factors, particularly any differences in plant characteristics that might lead to these differences. 

3.3.4.2 REPORTING AND DOCUMENTATION

It is good practice to document and archive all information required to produce the national emissions inventory 

estimates as outlined in Volume 1, Section 6.11. 

Some examples of specific documentation and reporting relevant to this source category are provided below: 

 

1

 In some cases, processes designed to reduce NOx emissions may result in additional N2O generation. Increased N2O 

concentrations due to NOx abatement technology have been measured at various power plants that employ non-catalytic 

reduction for NOx (Cook, 1999). From at least one nitric acid plant, it is known that NOx control resulted in increased N2O 

emissions (Burtscher, 1999). 
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3.26 2006 IPCC Guidelines for National Greenhouse Gas Inventories 

• Description of the method used; 

• Number of nitric acid plants; 

• Emission factors; 

• Production data; 

• Production capacity; 

• Number of plants using abatement technology; 

• Type of abatement technology, destruction efficiency, and utilisation; 

• Any other assumptions. 

Plant operators should supply this information to the inventory compiler for compilation, and also archive the 

information at the site. Plant operators should also log and archive the measurement frequencies and 

instrumental calibration records where actual plant measurements are made. 

Where there are only one or two producers in a country, activity data may be considered confidential. In this case, 

operators and the inventory compiler should determine the level of aggregation at which information can be 

reported while still protecting confidentiality. Detailed information including instrumentation records should still 

be archived at the plant level. 

It is not practical to include all documentation in the national inventory report. However, the inventory should 

include summaries of methods used and references to source data such that the reported emissions estimates are 

transparent and steps in their calculation may be retraced. 
Chapter 3: Chemical Industry Emissions 

2006 IPCC Guidelines for National Greenhouse Gas Inventories 3.27 

3.4 ADIPIC ACID PRODUCTION 

3.4.1 Introduction 

Adipic acid is used in the manufacture of a large number of products including synthetic fibres, coatings, plastics, 

urethane foams, elastomers and synthetic lubricants. The production of Nylon 6.6 accounts for the bulk of adipic 

acid use. As noted by Hocking (1998; p.657), ‘A large fraction of this consumption is direct, as adipic acid in the 

production of nylon 6.6, but a substantial fraction of the adipic acid is further processed to give hexamethylene 

diamine, the other monomer required. A further small fraction of the adipic acid is converted into di-octyl (di-2-

ethylhexyl) or di-hexyl esters for use as plasticizers in flexible grades of PVC, etc., or as a high boiling point 

component of synthetic motor oils’. 

3.4.2 Methodological issues 

Adipic acid is a dicarboxylic acid manufactured from a cyclohexanone/cyclohexanol mixture which is oxidised 

by nitric acid in the presence of a catalyst to form adipic acid. Nitrous oxide (N2O) is generated as an unintended 

by-product of the nitric acid oxidation stage: 

(CH2)5CO (Cyclohexanone) + (CH2)5CHOH (Cyclohexanol) + wHNO3 →

HOOC(CH2)4COOH (Adipic Acid) + xN2O + yH2O 

Adipic acid is a significant source of atmospheric N2O if not abated. Emissions of N2O depend on the amount 

generated in the production process and the amount destroyed in any subsequent abatement process. Abatement 

of N2O can be intentional through installation of equipment specifically designed to destroy N2O in adipic acid 

plants. Adipic acid production also results in the emissions of NMVOC, CO and NOx. Process emissions from 

the production of adipic acid vary substantially with the level of emission control employed. 

3.4.2.1 CHOICE OF METHOD

The decision tree in Figure 3.3 describes good practice in adapting the methods to national circumstances. 

Emissions can be estimated from continuous emissions monitoring (CEM) where emissions are directly 

measured at all times, periodic emissions monitoring that is undertaken over a period(s) that is reflective of the 

usual pattern of operation of the plant to derive an emission factor that is multiplied by output to derive 

emissions, irregular sampling to derive an emission factor that is multiplied by output to derive emissions, or by 

multiplying a default emission factor by output. 

Methods are classified according to the extent of plant-level data that are available. Both Tier 2 and Tier 3 

require plant-level activity data. 

TIER 1 METHOD 

Emissions are estimated as follows: 

EQUATION 3.7 

N2O EMISSIONS FROM ADIPIC ACID PRODUCTION – TIER 1 

EN2O = EF • AAP

Where: 

EN2O = N2O emissions, kg 

EF = N2O emission factor (default), kg N2O/tonne adipic acid produced 

AAP = adipic acid production, tonnes 

When applying the Tier 1 method it is good practice to assume that there is no abatement of N2O emissions and 

to use the highest default emission factor shown in Table 3.4. 
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3.28 2006 IPCC Guidelines for National Greenhouse Gas Inventories 

TIER 2 METHOD 

The Tier 2 method uses plant-level production data and default emission factors. Where default values are used 

to estimate emissions, it is good practice to categorise plants according to the abatement technology type 

employed and the utilisation factor of the abatement technology. Emissions are calculated as follows: 

EQUATION 3.8 

N2O EMISSIONS FROM ADIPIC ACID PRODUCTION – TIER 2 

= ∑[ ] • • ( ) − • i jEN O EFi AAPi DFj ASUFj , 2 1

Where: 

EN2O = emissions of N2O, kg 

EFi = N2O emission factor for technology type i, kg N2O/tonne adipic acid produced 

AAPi = adipic acid production from technology type i, tonnes 

DFj = destruction factor for abatement technology type j, fraction 

ASUFj = abatement system utilisation factor for abatement technology type j, fraction 

The basic equation for estimating N2O emissions includes additional terms that recognise the use of N2O 

abatement technologies. The N2O destruction factor has to be multiplied by an abatement system utilisation 

factor in order to account for any down-time of the emission abatement equipment (i.e., time the equipment is 

not operating). 

To achieve the highest accuracy, good practice is to apply this equation at the plant-level using N2O generation 

and destruction factors developed from plant-specific measurement data. In this case, the national total is equal 

to the sum of plant totals. Where plant-level information is not available, good practice provides default N2O 

generation factors and destruction factors as shown in Table 3.4, Default Factors for Adipic Acid Production, 

based on abatement technologies implemented. To use these factors, inventory compilers should verify that the 

abatement technology is installed at individual plants and operated throughout the year. 

TIER 3 METHOD – DIRECT MEASUREMENT 

The Tier 3 method uses plant level production data and plant-level emission factors obtained from direct 

measurement of emissions. These may be derived from irregular sampling of emissions of N2O or periodic 

emissions monitoring of N2O undertaken over a period(s) that reflects the usual pattern of operation of the plant. 

Emissions can be derived using Equation 3.8. To achieve the highest accuracy, good practice is to apply this 

equation at the plant-level using N2O generation and destruction factors developed from plant-specific 

measurement data where relevant. Given the relatively small number of adipic acid plants (about 23 globally, 

Choe et al., 1993), obtaining plant-specific information requires few additional resources. 

Alternatively, the Tier 3 method uses the results of continuous emissions monitoring (CEM), although it is noted 

that most plants are unlikely to employ CEM due to the resource costs. Where CEM is employed, emissions can 

be estimated based on the sum of measured N2O emissions derived from the concentration of N2O in monitored 

emissions for each recorded monitoring interval. 

3.4.2.2 CHOICE OF EMISSION FACTORS

TIER 1 METHOD 

It is good practice to use the default emission factor shown in Table 3.4 and to assume that there is no abatement 

of N2O emissions. 

TIER 2 METHOD 

If plant-level factors are not available, it is good practice to use default factors. The Tier 2 method is based on 

default emission factors. These default values often represent midpoint or mean values of data sets (as 

determined by expert analysis). The extent to which they represent a specific plant’s emission rate is unknown. 

Default factors in Table 3.4 should be used only in cases where plant-specific measurements are not available. 

Also included in Table 3.4 are default N2O destruction factors for commonly used abatement technologies, and 

associated uncertainties. To use these factors, inventory compilers should verify that the abatement technology is 

installed at individual plants and operated throughout the year. Failure to determine if abatement technologies 
Chapter 3: Chemical Industry Emissions 

2006 IPCC Guidelines for National Greenhouse Gas Inventories 3.29 

are being used can result in overestimation of emissions. Determination of the appropriate values requires that 

plants be classified according to the abatement technology implemented.. 

TIER 3 METHOD 

The Tier 3 method requires plant measurements. If the N2O abatement system is in use, plant measurements 

provide the most rigorous data for calculating net emissions (i.e., N2O generation and destruction factors). 

Monitoring N2O emissions from adipic acid production is practical because these are point sources and there are 

a finite number of production plants. Given currently available technology, instrumentation for sampling and 

monitoring emission rates do not limit precision or accuracy of the overall measurement. Usually sampling 

frequency and timing is sufficient to avoid systematic errors and to achieve the desired level of accuracy. 

Where the N2O abatement system is not in use, a plant-specific emission factor can be obtained from periodic 

monitoring of emissions which is multiplied by the production level to estimate plant-level emissions. 

As a general rule, it is good practice to conduct sampling and analysis whenever a plant makes any significant 

process changes that would affect the generation rate of N2O, and sufficiently often otherwise to ensure that 

operating conditions are constant. In addition, plant operators should be consulted annually to determine the 

specific destruction technologies employed and confirm their use, since technologies may change over time. 

Precise measurement of the emissions rate and abatement efficiencies requires measurement of both the exit 

stream and the uncontrolled stream. Where measurement data are available only on the exit stream, good 

practice is to base emissions on these data. In this case, any available estimates of abatement efficiency should 

be provided only for information purposes and not used to calculate emissions. 

Figure 3.3 Decision tree for estimation of N2O emissions from adipic acid production 

Start

Are direct

measurement data

available?

Is this a key

category1?

Are

plant- specific

activity data available on adipic 

acid production?

Yes

No

No

Collect data for the Tier 3

or Tier 2 method.

Use plant specific-emissions data

and activity data (irregular sampling

data, periodic monitoring data or 

continuous emissions monitoring) as 

basis for Tier 3 method.

Use plant-specific data on quantity

of adipic acid produced as basis for 

Tier 2 method.

Use national data on adipic acid 

production or national data on

capacity, and default emission factors.

Box 1: Tier 1

Box 2: Tier 2

Box 3: Tier 3

Note:

1. See Volume 1 Chapter 4, Methodological Choice and Identification of Key Categories (noting Section 4.1.2 on limited resources), for 

discussion of key categories and use of decision trees.

Yes

No

Yes
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3.30 2006 IPCC Guidelines for National Greenhouse Gas Inventories 

TABLE 3.4 

DEFAULT FACTORS FOR ADIPIC ACID PRODUCTION

Production 

Process 

N2O Generation 

Factora,d

Uncertainty Estimate 

Nitric Acid 

Oxidation 

300 kg/tonne 

adipic acid 

(uncontrolled) 

± 10% (based on expert judgement). The range of 300 kg ± 10% 

encompasses the variability from pure ketone to pure alcohol feedstocks, 

with most manufacturers somewhere in the middle.a

Abatement 

Technology 

N2O Destruction 

Factorb 

Uncertainty Estimate 

Catalytic 

Destruction 

92.5% 90-95% (based on expert judgement). Manufacturers known to employ this 

technology include: BASF (Scott, 1998), and DuPont (Reimer, 1999b). 

Thermal 

Destruction 

98.5% 98-99% (based on expert judgement). Manufacturers known to employ this 

technology include: Asahi, DuPont, Bayer, and Solutia (Scott, 1998). 

Recycle to 

Nitric Acid 

98.5% 98-99% (based on expert judgement). Manufacturers known to employ this 

technology include: Alsachemie (Scott, 1998). 

Recycle to 

feedstock for 

Adipic Acid 

94% 90-98% (based on expert judgement). Solutia implemented this technology 

around 2002. 

Abatement 

System 

Utilisation Factord Uncertainty Estimate 

Catalytic 

Destruction 

89% 80-98% (based on expert judgement)c. 

Thermal 

Destruction 

97% 95-99% (based on expert judgement)c. 

Recycle to 

Nitric Acid 

94% 90-98% (based on expert judgement)c. 

Recycle to 

Adipic Acid 

89% 80-98% (based on expert judgement)c. 

a

 With regard to a value from the Japan Environment Agency (1995) (282 kg N2O/tonne adipic acid), it is believed that this 

manufacturer uses oxidation of pure cyclohexanol (alcohol), instead of a ketone-alcohol mixture (Reimer et al., 1999). This is the only 

plant known to use this method. 

b

 The destruction factor (that represents the technology abatement efficiency) should be multiplied by an abatement system utility 

factor. 

c

 Note that these default values are based on expert judgement and not industry-supplied data or plant-specific measurements. In the first 

1-5 years of the abatement technology implementation, the utilisation factor tends to be at the lower end of the range. Lower utility of 

the equipment typically results because of the need to learn how to operate the abatement system and because more maintenance 

problems occur during the initial phase. After 1-5 years, the operating experience improves and the utilisation factor would tend to be 

at the high end of the range. 

Source: 

d

 Thiemans and Trogler (1991). 

e

 Reimer (1999b). 

3.4.2.3 CHOICE OF ACTIVITY DATA

It is good practice to compile production data at a level of detail that allows the use of a Tier 2 or Tier 3 method. 

TIER 1 METHOD 

The Tier 1 method requires data on national production of adipic acid. If national-level activity data are not 

available, information on production capacity can be used. It is good practice to multiply the total national 

production capacity by a capacity utilisation factor of 80 percent ± 10 percent (i.e., a range of 70-90 percent). 

TIER 2 METHOD 

The Tier 2 method requires plant-level production data disaggregated by abatement technology type. It is good 

practice to gather activity (production) data at a level of detail consistent with that of any generation and 

destruction data. Typical plant-level production data is accurate to ±2 percent due to the economic value of 

having accurate information. 
Chapter 3: Chemical Industry Emissions 

2006 IPCC Guidelines for National Greenhouse Gas Inventories 3.31 

TIER 3 METHOD 

As with the Tier 2 method, plant-level production data disaggregated by abatement technology type are required 

when emissions estimates are derived using data from irregular or periodic sampling of emissions. It is good 

practice to gather activity (production) data at a level of detail consistent with that of any generation and 

destruction data. Although production is not used in the estimation of emissions where the estimate is based on 

CEM, these data should be collected and reported to ensure that changes in variables that influence emissions 

can be monitored over time. Typical plant-level production data is accurate to ±2 percent due to the economic 

value of having accurate information. 

3.4.2.4 COMPLETENESS

Complete coverage for the adipic acid source category is straightforward because of the small number of readily 

identifiable plants. 

3.4.2.5 DEVELOPING A CONSISTENT TIME SERIES

N2O emissions should be recalculated for all years whenever emission calculation methods are changed (e.g., if 

the inventory compiler changes from the use of default values to actual values determined at the plant level). If 

plant-specific data are not available for all years in the time series, it will be necessary to consider how current 

plant measurements can be used to recalculate emissions for previous years. It may be possible to apply current 

plant-specific emission factors to production data from previous years, provided that plant operations have not 

changed substantially. Such a recalculation is required to ensure that any changes in emissions trends are real 

and not an artefact of changes in procedure. It is good practice to recalculate the time series according to the 

guidance provided in Volume 1, Chapter 5. 

3.4.3 Uncertainty assessment 

3.4.3.1 EMISSION FACTOR UNCERTAINTIES

Uncertainties for the default values shown in Table 3.4 are estimates based on expert judgement. In general, 

adipic acid default emission factors are relatively certain because they are derived from the stoichiometry of an 

intended chemical reaction (nitric acid oxidation) and N2O-specific abatement systems. The uncertainty in the 

emission factor for adipic acid represents a variability in N2O generation due to differences in the composition of 

the cyclohexanone and cyclohexanol feedstock (i.e. ketone and alcohol) that are used by different manufacturers. 

Higher ketone content results in increased N2O generation, whereas higher alcohol content results in less N2O 

generation (Reimer, 1999a). Dependent on the process, based on nitric acid (HNO3) consumption an individual 

plant should be able to determine the production of N2O within 1 percent. Uncertainties for the default values are 

shown in Table 3.4. 

3.4.3.2 ACTIVITY DATA UNCERTAINTIES

Potential N2O emissions per metric tonne produced are far greater for adipic acid production than for other 

industrial sources of N2O. Measurements obtained from a properly maintained and calibrated monitoring system 

can determine emissions using Equation 3.8 to within ±5 percent at the 95 percent confidence level. Given the 

small number of adipic acid plants, the uncertainty in national production data (Tier 1) is the same as for plantlevel data, namely, ±2 percent. 

3.4.4 Quality Assurance/Quality Control (QA/QC), 

Reporting and Documentation 

3.4.4.1 QUALITY ASSURANCE/QUALITY CONTROL

It is good practice to conduct quality control checks as outlined in Volume 1, Chapter 6, and an expert review of 

the emissions estimates. Additional quality control checks as outlined in Volume 1 and quality assurance 

procedures may also be applicable, particularly if higher tier methods are used to determine emissions from this 
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3.32 2006 IPCC Guidelines for National Greenhouse Gas Inventories 

source category. Inventory compilers are encouraged to use higher tier QA/QC for key categories as identified in 

Volume 1, Chapter 4. 

In addition to the guidance in Volume 1, specific procedures of relevance to this source category are outlined 

below. 

Comparison of emissions estimates using different approaches 

If emissions are calculated using data from individual adipic acid plants (bottom-up approach), inventory 

compilers should compare the estimate to emissions calculated using national production data (top-down 

approach). They should record the results and investigate any unexplained discrepancies. 

Since industrial N2O source categories are relatively small compared to other anthropogenic and natural sources, 

it is not feasible to compare emissions with measured trends in atmospheric N2O concentrations. 

Plant-level data 

Inventory compilers should archive sufficient information to allow an independent review of the time series of 

emissions beginning in the base year, and to explain trends in emissions when making historical comparisons. 

This is particularly important in cases where recalculations are necessary, for example, when an inventory 

compiler changes from using default values to actual values determined at the plant level. 

Revision of direct emission measurements 

If plant-level N2O measurements are available, it is suggested that inventory compilers confirm that 

internationally recognised, standard methods were used. If the measurement practices fail this criterion, then they 

should evaluate the use of these emissions data. In addition, they should reconsider the uncertainty estimates in 

light of the QA/QC results. 

Inventory compilers are encouraged to compare plant-based factors to the IPCC defaults to ensure that the plantspecific factors are reasonable. They should explain and document any differences between plant-specific factors 

and default factors, particularly any differences in plant characteristics that might lead to these differences. 

3.4.4.2 REPORTING AND DOCUMENTATION

It is good practice to document and archive all information required to produce the national emissions inventory 

estimates as outlined in Volume 1, Section 6.11. 

Some examples of specific documentation and reporting relevant to this source category are provided below: 

• Description of the method used; 

• Number of adipic acid plants; 

• Emission factors; 

• Production data; 

• Production capacity; 

• Number of plants using abatement technology; 

• Type of abatement technology, destruction efficiency, and utilisation; 

• Any other assumptions. 

Plant operators should supply this information to the inventory compiler for compilation, and also archive the 

information at the site. Plant operators should also log and archive the measurement frequencies and 

instrumental calibration records where actual plant measurements are made. 

Where there are only one or two producers in a country, as could often be the case for adipic acid production, 

activity data may be considered confidential. In this case, operators and the inventory compiler should determine 

the level of aggregation at which information can be reported while still protecting confidentiality. Detailed 

information including instrumentation records should still be archived at the plant level. 

It is not practical to include all documentation in the national inventory report. However, the inventory should 

include summaries of methods used and references to source data such that the reported emissions estimates are 

transparent and steps in their calculation may be retraced. 
Chapter 3: Chemical Industry Emissions 

2006 IPCC Guidelines for National Greenhouse Gas Inventories 3.33 

3.5 CAPROLACTAM, GLYOXAL AND GLYOXYLIC 

ACID PRODUCTION 

3.5.1 Introduction 

This section addresses the production of three chemicals - caprolactam, glyoxal, and glyoxylic acid - that are 

potentially important sources of nitrous oxide (N2O) emissions in the countries in which the chemicals are 

produced. The methodology for caprolactam is discussed in detail and is suitable for application to estimation of 

emissions from glyoxal and glyoxylic acid. In Section 3.5.3, the production processes for glyoxal and glyoxylic 

acid that give rise to emissions of N2O are outlined. Default generation factors, destruction factors, and emission 

factors are provided based on information from Clariant (France) (Babusiaux, 2005). 

3.5.2 Caprolactam 

Almost all of the annual production of caprolactam (C6H11NO) is consumed as the monomer for nylon-6 fibres 

and plastics (Kirk-Othmer, 1999; p.310), with a substantial proportion of the fibre used in carpet manufacturing. 

All commercial processes for the manufacture of caprolactam are based on either toluene or benzene. 

3.5.2.1 METHODOLOGICAL ISSUES

Where caprolactam is produced from benzene, the main process, the benzene is hydrogenated to cyclohexane 

which is then oxidised to produce cyclohexanone (C6H10O). The classical route (Raschig process) and basic 

reaction equations for production from cyclohexanone are (Reimschuessel, 1977; p.83: Lowenheim and Moran, 

1975; p. 201): 

Oxidation of NH3 to NO/NO2

↓

NH3 reacted with CO2/H2O to yield ammonium carbonate (NH4)2CO3

↓

(NH4)2CO3 reacted with NO/NO2 (from NH3 oxidation) to yield ammonium nitrite (NH4NO2) 

↓

NH3 reacted with SO2/H2O to yield ammonium bisulphite (NH4HSO3) 

↓

NH4NO2 and NH4HSO3 reacted to yield hydroxylamine disulphonate (NOH(SO3NH4)2) 

↓

NOH(SO3NH4)2 hydrolised to yield hydroxylamine sulphate (NH2OH)2.H2SO4) and ammonium 

sulphate ((NH4)2SO4) 

↓

Cyclohexanone reaction: 

C6H10O + 1⁄2(NH2OH)2.H2SO4 (+NH3 and H2SO4) → C6H10NOH + (NH4)2SO4 + H2O 

Beckmann rearrangement: 

C6H10NOH (+H2SO4 and SO2) → C6H11NO.H2SO4 (+4NH3 and H2O) → C6H11NO + 2(NH4)2SO4

Lowenheim and Moran (1975; p. 202) summarise the Raschig production process as follows. Caprolactam is 

produced via Beckmann rearrangement (conversion of a ketone oxime into an amide, usually using sulphuric 

acid as a catalyst) by the addition of hydroxylamine sulphate to cyclohexanone. Hydroxylamine sulphate is 

produced from ammonium nitrate and sulphur dioxide. Ammonia gas and air are fed to a converter where 

ammonia is converted to hydroxylamine disulphonate by contacting it with ammonium carbonate and sulphur 

dioxide in series. Ammonium carbonate is produced by dissolving ammonia and carbon dioxide in water, and 

sulphur dioxide by burning sulphur. The disulphonate is hydrolysed to hydroxylamine sulphate and ammonium 

sulphate. The addition of hydroxylamine sulphate to cyclohexanone produces cyclohexanone oxime which is 

converted to caprolactam by the Beckmann rearrangement. 
Volume 3: Industrial Processes and Product Use 

3.34 2006 IPCC Guidelines for National Greenhouse Gas Inventories 

Production of caprolactam can give rise to emissions of nitrous oxide (N2O) from the ammonia oxidation step, 

emissions of CO2 from the ammonium carbonate step, emissions of sulphur dioxide (SO2) from the ammonium 

bisulphite step, and emissions of NMVOCs. Emissions of CO2, SO2 and NMVOCs from the conventional 

process are unlikely to be significant in well-managed plants. The main greenhouse gas to be accounted for from 

caprolactam production is N2O. Modified caprolactam production processes are primarily concerned with 

elimination of the high volumes of ammonium sulphate that are produced as a by-product of the conventional 

process (Reimschuessel, 1977; p.84). NH3 oxidation remains an integral part of all processes to obtain the 

NO/NO2 required. 

CHOICE OF METHOD 

Estimation of emissions of N2O from caprolactam production can be treated as analogous to estimation of 

emissions of N2O from nitric acid production. Both production processes involve an initial step of NH3 oxidation 

which is the source of N2O formation and emissions. 

The choice of good practice method depends on national circumstances. The decision tree in Figure 3.4 

describes good practice in adapting the methods to national circumstances. Emissions can be estimated from 

continuous emissions monitoring (CEM) where emissions are directly measured at all times, periodic emissions 

monitoring that is undertaken over a period(s) that is reflective of the usual pattern of operation of the plant to 

derive an emission factor that is multiplied by output to derive emissions, irregular sampling to derive an 

emission factor that is multiplied by output to derive emissions, or by multiplying a default emission factor by 

output. 

Methods are classified according to the extent of plant-level data that are available. Both Tier 2 and Tier 3 are 

require plant-level activity data. 

Tier 1 method 

Emissions are estimated as follows: 

EQUATION 3.9 

N2O EMISSIONS FROM CAPROLACTAM PRODUCTION – TIER 1 

EN2O = EF •CP

Where: 

EN2O = N2O emissions, kg 

EF = N2O emission factor (default), kg N2O/tonne caprolactam produced 

CP = caprolactam production, tonnes 

When applying the Tier 1 method it is good practice to assume that there is no abatement of N2O emissions and 

to use the highest default emission factor shown in Table 3.5. 

Tier 2 method 

Information on emissions arising from caprolactam production and control technologies is limited. Where plantlevel information is not available, good practice provides default N2O generation factors as shown in Table 3.5. 

The default factors are based on N2O emissions from nitric acid plants because there is no information on 

caprolactam plants and the initial reaction step of oxidation of ammonia is similar for both processes. Good 

practice encourages the development of factors specific to caprolactam plants. 

The number of caprolactam plants is relatively small (approximately 42 plants with around 19 plants using DSM 

(Stamicarbon) technology). It is unlikely that there are substantial variations in the N2O generation factors 

between plants. Where default values are used to estimate emissions from caprolactam production, it is good 

practice to ascertain the extent to which plant emissions vary according to type and to use an appropriate N2O 

generation factor. 

The Tier 2 method uses plant-level production data disaggregated by technology type and default emission 

factors classified by technology type. Emissions are calculated as follows: 
Chapter 3: Chemical Industry Emissions 

2006 IPCC Guidelines for National Greenhouse Gas Inventories 3.35 

EQUATION 3.10 

N2O EMISSIONS FROM CAPROLACTAM PRODUCTION – TIER 2 

= ∑[ • • ( ) − • ]

i j

EN O EFi CPi DFj ASUFj , 2 1

Where: 

EN2O = emissions of N2O, kg 

EFi = N2O emission factor for technology type i, kg N2O/tonne caprolactam produced 

CPi = caprolactam production from technology type i, tonnes 

DFj = destruction factor for abatement technology type j, fraction 

ASUFj = abatement system utilisation factor for abatement technology type j, fraction 

The basic equation for estimating N2O emissions includes additional terms that recognise current and the 

potential future use of N2O abatement technologies. The N2O destruction factor has to be multiplied by an 

abatement system utilisation factor in order to account for any down-time of the emission abatement equipment 

(i.e. time the equipment is not operating). 

Where plant-level information is not available, good practice provides default N2O generation factors as shown 

in Table 3.5, Default Factors for Caprolactam Production, based on plant types classified by age. To achieve the 

highest accuracy, good practice is to apply Equation 3.10 at the plant-level taking into account N2O generation 

and destruction factors developed from plant-specific measurement data. In this case, the national total is equal 

to the sum of plant totals. 

Tier 3 method – direct measurement 

The Tier 3 method uses plant level production data and plant-level emission factors obtained from direct 

measurement of emissions. These may be derived from irregular sampling of emissions of N2O or periodic 

emissions monitoring of N2O undertaken over a period(s) that reflects the usual pattern of operation of the plant. 

Emissions can be derived using Equation 3.10. 

Alternatively, the Tier 3 method uses the results of continuous emissions monitoring (CEM), although it is noted 

that most plants are unlikely to employ CEM due to the resource costs. Where CEM is employed, emissions can 

be estimated based on the sum of measured N2O emissions derived from the concentration of N2O in monitored 

emissions for each recorded monitoring interval. 

CHOICE OF EMISSION FACTORS 

Tier 1 method 

It is good practice to use the emission factor shown in Table 3.5 and to assume that there is no abatement of N2O 

emissions. 

Tier 2 method 

If plant-level factors are not available, it is good practice to use default factors. The Tier 2 method uses a default 

factor. Default values often represent midpoint or mean values of data sets (as determined by expert analysis). 

The extent to which they represent a specific plant’s emission rate is unknown. This is especially true for 

caprolactam production where the value is based on high pressure nitric acid plants. Default factor in Table 3.5 

should be used only in cases where plant-specific measurements are not available. 

Tier 3 method 

Plant measurements provide the most rigorous data for calculating net emissions (i.e., N2O generation and 

destruction factors). Monitoring N2O emissions from caprolactam production is practical because these are point 

sources and there are a finite number of production plants. Given currently available technology, instrumentation 

for sampling and monitoring emission rates do not limit precision or accuracy of the overall measurement. 

Usually sampling frequency and timing is sufficient to avoid systematic errors and to achieve the desired level of 

accuracy. 

As a general rule, it is good practice to conduct sampling and analysis whenever a plant makes any significant 

process changes that would affect the generation rate of N2O, and sufficiently often otherwise to ensure that 

operating conditions are constant. In addition, plant operators should be consulted annually to determine the 

specific destruction technologies employed and confirm their use, since technologies may change over time. 

Precise measurement of the emissions rate and abatement efficiencies requires measurement of both the exit 
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3.36 2006 IPCC Guidelines for National Greenhouse Gas Inventories 

stream and the uncontrolled stream. Where measurement data are available only on the exit stream, good 

practice is to base emissions on these data. In this case, any available estimates of abatement efficiency should 

be provided only for information purposes and not used to calculate emissions. 

TABLE 3.5 

DEFAULT FACTOR FOR CAPROLACTAM PRODUCTION

Production Process N2O Emission Factor 

(kg N2O/tonne caprolactam) 

Uncertainty 

Raschig 9.0a ± 40% 

a

 Based on high pressure plants for nitric acid production. 

Source: Default Factors for Nitric Acid Production. (See Table 3.3 in this chapter.) 

Figure 3.4 Decision tree for estimation of N2O emissions from caprolactam, glyoxal or 

glyoxylic acid production 

Start

Are direct

measurement data

available?

Is Caprolactam,

Glyoxal and Glyoxylic

Acid Production a key category1

,

and is this a significant

subcategory?

Are

plant-specific activity

data available on caprolactam, 

glyoxal or glyoxylic acid

production?

Yes

No

No

Collect data for the Tier 3

or Tier 2 method.

Use plant specific-emissions data

and activity data (irregular sampling

data, periodic monitoring data or 

continuous emissions monitoring) as 

basis for Tier 3 method.

Use plant-specific data on quantity of 

caprolactam, glyoxal or glyoxylic acid 

produced as basis for Tier 2 method.

Use national data on caprolactam, 

glyoxal or glyoxylic acid production

or national data on capacity, and

default emission factors.

Box 1: Tier 1

Box 2: Tier 2

Box 3: Tier 3

Note:

1. See Volume 1 Chapter 4, Methodological Choice and Identification of Key Categories (noting Section 4.1.2 on limited resources), for 

discussion of key categories and use of decision trees.

No

Yes

Yes
Chapter 3: Chemical Industry Emissions 

2006 IPCC Guidelines for National Greenhouse Gas Inventories 3.37 

CHOICE OF ACTIVITY DATA 

It is good practice to compile production data at a level of detail that allows the use of Tier 2 or Tier 3 method. 

Tier 1 method 

The Tier 1 method requires data on national production of caprolactam. If national-level activity data are not 

available, information on production capacity can be used. It is good practice to multiply the total national 

production capacity by a capacity utilisation factor of 80 percent ± 20 percent (i.e., a range of 60-100 percent). 

Tier 2 method 

The Tier 2 method requires plant-level production data disaggregated by the age the plant. If additional 

information on technology type and abatement technology is available, it is good practice to collect this 

information and disaggregate production data according to the information obtained. That is, it is good practice

to gather activity (production) data at a level of detail consistent with that of generation and destruction data. 

Where plant-level emission factors are used, good practice is to collect plant-level production data. Typical 

plant-level production data are accurate to ±2 percent due to the economic value of having accurate information. 

Tier 3 method 

The Tier 3 method require plant-level production data disaggregated by technology type when emissions 

estimates are derived using data from irregular or periodic sampling of emissions. It is good practice to collect 

activity (production) data at a level of detail consistent with that of any generation and destruction data. 

Although production is not used in the estimation of emissions where the estimate is based on CEM, these data 

should be collected and reported to ensure that changes in variables that influence emissions can be monitored 

over time. Typical plant-level production data are accurate to ±2 percent due to the economic value of having 

accurate information. 

COMPLETENESS 

Complete coverage requires accounting for all plants and emissions of all direct greenhouse gases. In addition to 

N2O, there may be non-combustion emissions of CO2, NOx, NMVOCs and SO2. In order to include emissions of 

the indirect greenhouse gases (NOx, NMVOCs and SO2), see guidance provided in Chapter 7 of Volume 1: 

General Guidance and Reporting. Plant-level information will be required to enable emissions estimation. Over 

time default values could be developed as more information becomes available. 

There will be few caprolactam plants in a country, and it is suggested that emissions are calculated from plant 

specific data. 

DEVELOPING A CONSISTENT TIME SERIES 

N2O emissions should be recalculated for all years whenever emission calculation methods are changed (e.g., if 

the inventory compiler changes from the use of default values to actual values determined at the plant level). If 

plant-specific data are not available for all years in the time series, it will be necessary to consider how current 

plant measurements can be used to recalculate emissions for previous years. It may be possible to apply current 

plant-specific emission factors to production data from previous years, provided that plant operations have not 

changed substantially. Such a recalculation is required to ensure that any changes in emissions trends are real 

and not an artefact of changes in procedure. It is good practice to recalculate the time series according to the 

guidance provided in Volume 1, Chapter 5. 

3.5.2.2 UNCERTAINTY ASSESSMENT

EMISSION FACTOR UNCERTAINTIES 

Uncertainties for the default value shown in Table 3.5 is an estimate based on default values for nitric acid plants. 

In general, default emission factors for gaseous substances have higher uncertainties because mass values for 

gaseous substances are influenced by temperature and pressure variations and gases are more easily lost through 

process leaks. The default values for caprolactam production have a relatively high level of uncertainty due to 

the limited information available. It is good practice to obtain uncertainty estimates at the plant-level which 

should be lower than uncertainty values associated with default values. 

ACTIVITY DATA UNCERTAINTIES 

Where activity data are obtained from plants, uncertainty estimates can be obtained from producers. Data that are 

obtained from national statistical agencies usually do not include uncertainty estimates. It is good practice to 

consult with national statistical agencies to obtain information on any sampling errors. Where national statistical 
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3.38 2006 IPCC Guidelines for National Greenhouse Gas Inventories 

agencies collect data from the population of nitric acid production facilities, uncertainties in national statistics 

are not expected to differ from uncertainties established from plant-level consultations. Where uncertainty values 

are not available from other sources, a default value of ±2 percent can be used. 

3.5.2.3 QUALITY ASSURANCE/QUALITY CONTROL (QA/QC),

REPORTING AND DOCUMENTATION

QUALITY ASSURANCE/QUALITY CONTROL 

It is good practice to conduct quality control checks as outlined in Volume 1, Chapter 6. More extensive quality 

control checks and quality assurance procedures are applicable if higher tier methods are used to determine 

emissions. Inventory compilers are encouraged to use higher tier QA/QC for key categories as identified in 

Volume 1, Chapter 4. 

Comparison of emissions estimates using different approaches 

If emissions are calculated using data from individual caprolactam plants (bottom-up approach), inventory 

compilers should compare the estimate to emissions calculated using national production data (top-down 

approach). They should record the results and investigate any unexplained discrepancies. 

Since industrial N2O source categories are relatively small compared to other anthropogenic and natural sources, 

it is not feasible to compare emissions with measured trends in atmospheric N2O concentrations. 

Plant-level data 

Inventory compilers should archive sufficient information to allow an independent review of the time series of 

emissions beginning in the base year, and to explain trends in emissions when making historical comparisons. 

This is particularly important in cases where recalculations are necessary, for example, when an inventory 

compiler changes from using default values to actual values determined at the plant level. 

Revision of direct emission measurements 

If plant-level N2O measurements are available, inventory compilers should confirm that internationally 

recognised, standard methods were used. If the measurement practices fail this criterion, then they should 

evaluate the use of these emissions data. In addition, they should reconsider the uncertainty estimates in light of 

the QA/QC results. 

Inventory compilers should compare plant-based factors to the IPCC defaults to ensure that the plant-specific 

factors are reasonable. They should explain and document any differences between plant-specific factors and 

default factors, particularly any differences in plant characteristics that might lead to these differences. 

REPORTING AND DOCUMENTATION 

It is good practice to document and archive all information required to produce the national emissions inventory 

estimates as outlined in Volume 1, Section 6.11. 

Some examples of specific documentation and reporting relevant to this source category are provided below: 

• Description of the method used; 

• Number of caprolactam plants; 

• Emission factors; 

• Production data; 

• Production capacity; 

• Number of plants using abatement technology; 

• Type of abatement technology, destruction efficiency, and utilisation; 

• Any other assumptions. 

Plant operators should supply this information to the inventory compiler for compilation, and also archive the 

information at the site. Plant operators should also log and archive the measurement frequencies and 

instrumental calibration records where actual plant measurements are made. 

Where there are only one or two producers in a country as will be the case for caprolactam producers, activity 

data may be considered confidential. In this case, operators and the inventory compiler should determine the 
Chapter 3: Chemical Industry Emissions 

2006 IPCC Guidelines for National Greenhouse Gas Inventories 3.39 

level of aggregation at which information can be reported while still protecting confidentiality. Detailed 

information including instrumentation records should still be archived at the plant level. 

It is not practical to include all documentation in the national inventory report. However, the inventory should 

include summaries of methods used and references to source data such that the reported emissions estimates are 

transparent and steps in their calculation may be retraced. 

3.5.3 Glyoxal and glyoxylic acid production 

Glyoxal (ethanedial) (C2H2O2) is produced from oxidation of acetaldehyde (ethanal) (C2H4O) with concentrated 

nitric acid (HNO3). Glyoxal can also be produced from catalytic oxidation of ethylene glycol (ethanediol) 

(CH2OHCH2OH). Glyoxal is used as a crosslinking agent for vinyl acetate/acrylic resins, disinfectant, gelatine 

hardening agent, textile finishing agent (permanent-press cotton, rayon fabrics), wet-resistance additive (paper 

coatings) (Ashford, 1994; p.454). 

Glyoxylic acid is produced by nitric acid oxidation of glyoxal. Glyoxylic acid is used for the production of 

synthetic aromas, agrochemicals and pharmaceutical intermediates (Babusiaux, 2005; p.1). 

The basic reaction equation for the production of glyoxal from acetaldehyde is: 

2C2H4O (Acetaldehyde) + 2HNO3 → 2C2H2O2 (Glyoxal) + N2O + H2O 

The stoichiometric relationship indicates that complete reaction will result in 0.543 tonnes of N2O per tonne of 

glyoxal. Under commercial conditions, the yield of N2O per tonne of glyoxal is approximately 0.52 tonnes 

(Babusiaux, 2005; p.1). 

Glyoxylic acid production is a batch process where nitric acid is reduced to NO and N2O with NO recovered as 

HNO3 in the process. N2O arises in the production process through a secondary reaction where glyoxal is 

converted to oxalic acid (COOH)2. 

Default factors for glyoxal and glyoxylic acid production are shown in Table 3.6. Emissions can be estimated 

using the same approach as described in the foregoing for caprolactam. To use default destruction factors, 

inventory compilers should verify that the abatement technology is installed at individual plants and operated 

throughout the year. 

TABLE 3.6 

DEFAULT FACTORS FOR GLYOXAL AND GLYOXYLIC ACID PRODUCTION

Product N2O Generation Factor 

(tonnes N2O/tonne) 

N2O Destruction Rate 

(%) 

N2O Emission Factor 

(tonnes N2O/tonne) 

Uncertainty 

(%) 

Glyoxal 0.52 80 0.10 ±10 

Glyoxylic acid 0.10 80 0.02 ±10 

Source: Babusiaux (2005) 
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3.40 2006 IPCC Guidelines for National Greenhouse Gas Inventories 

3.6 CARBIDE PRODUCTION 

3.6.1 Introduction 

Greenhouse gas emissions are associated with production of silicon carbide (SiC) and calcium carbide (CaC2). 

The production of carbide can result in emissions of carbon dioxide (CO2), methane (CH4), carbon monoxide 

(CO) and sulphur dioxide (SO2). Silicon carbide is a significant artificial abrasive. It is produced from silica sand 

or quartz and petroleum coke. Calcium carbide is used in the production of acetylene, in the manufacture of 

cyanamide (a minor historical use), and as a reductant in electric arc steel furnaces. It is made from two carboncontaining raw materials: calcium carbonate (limestone) and petroleum coke. 

Use of carbon-containing raw materials in the production processes result in emissions of CO2 and CO. The 

presence of hydrogen-containing volatile compounds and sulphur (S) in the petroleum coke may cause formation 

and emission to the atmosphere of CH4 and SO2. 

3.6.2 Methodological issues 

CO2 AND CH4 FROM SILICON CARBIDE PRODUCTION 

Silicon carbide is produced from silica sand or quartz and petroleum coke, which is used as a carbon source, 

according to the reactions (Austin, 1984; p. 262): 

SiO2 + 2C → Si + 2CO 

Si + C → SiC 

The formula describing the overall reaction is given below but in practice it does not proceed in the 

stoichiometric proportions indicated: 

SiO2 + 3C → SiC + 2CO (+ O2 → 2CO2) 

In the production process, silica sand and carbon are mixed in an approximate molar ratio of 1:3. Some carbon, 

about 35 percent, is contained in the product and the rest is converted to CO2 in excess oxygen and released to 

the atmosphere as a process by-product. 

The petroleum coke used in this process may contain volatile compounds, which will form methane. Some 

methane will escape to the atmosphere, particularly during start-up. 

CO2 FROM CALCIUM CARBIDE PRODUCTION 

Calcium carbide (CaC2) is made by heating calcium carbonate (limestone) and subsequently reducing CaO with 

carbon e.g., petroleum coke. Both steps lead to emissions of CO2. Around 67 percent of the carbon from 

petroleum coke will be contained in the product. 

The basic reactions are: 

CaCO3 → CaO + CO2

CaO + 3C → CaC2 + CO (+ 1⁄2 O2 → CO2) 

The CO gas will be used as an energy source in most plants. 

BOX 3.4 

DOUBLE COUNTING

To avoid double counting, CO2 emission from combusting CO gas generated in the process of 

CaC2 production should be accounted in the IPPU Sector, and should not be included in the 

Energy Sector. Petroleum coke used in the production process should be deducted from the 

Energy Sector as a non-energy use of petroleum coke. 

The most important application of calcium carbide is producing acetylene (C2H2) by reacting CaC2 with water. A 

substantial use of acetylene is welding applications. Acetylene is also used in chemical synthesis for the 
Chapter 3: Chemical Industry Emissions 

2006 IPCC Guidelines for National Greenhouse Gas Inventories 3.41 

production of acetaldehyde, acetic acid, acetic anhydride, and as a feedstock to manufacture ‘acetylene black’, a 

form of carbon black. Frequently, acetylene is not produced within the same plant that produces CaC2 and this 

needs to be taken into account when applying higher tier methods to estimating CO2 emissions from CaC2 use. 

Use of acetylene in chemical synthesis and production of acetylene black results in carbon contained in the 

products reducing the total emissions of CO2 that are related to CaC2 use. Acetylene may be produced from 

partial oxidation of natural gas as well as from CaC2. The approach to accounting for acetylene in these uses is 

outlined in Section 3.9 of this volume. 

Production and use of acetylene for welding applications is summarised by reaction: 

CaC2 + 2H2O → Ca(OH)2 + C2H2 (+ 2.5O2 → 2CO2 + H2O) 

Where acetylene is used in welding applications, emissions can be derived from the quantity of CaC2 used in the 

production of this acetylene on the assumption that the acetylene will be used in a relatively short period of time 

after production. 

BOX 3.5 

ALLOCATION OF EMISSIONS FROM CaO PRODUCTION

CaO (lime) might be produced in-house or at a plant other than the carbide plant. In either case, the 

emissions from the CaO step should be reported as emissions from lime production (Section 2.3 of 

this volume) and only the emissions from reaction of CaO with petroleum coke and use of the 

product to produce acetylene for welding applications should be reported as emissions from 

calcium carbide. 

3.6.2.1 CHOICE OF METHOD

Methods are classified according the extent of plant-level data that are available. The Tier 1 method is based on 

default values and national statistics. Tier 2 is based on plant-level data on production and use of CaC2 in 

acetylene production for welding applications. The Tier 3 method is based on plant-level data on petroleum coke 

input (including the carbon content factor (CCF) and carbon oxidation factor (COF) if available; alternatively, 

country specific Energy Sector values may be used), use of CaC2 in acetylene production for welding 

applications, and plant-level emission factors where relevant. 

Both Tier 2 and Tier 3 are based on plant-level activity data. The choice of method to estimate emissions of CO2

and CH4 depends on national circumstances as shown in Figure 3.5. 

CO2 AND CH4 FROM CARBIDE PRODUCTION 

Tier 1 method 

Emissions from carbide production can be estimated from activity data (AD) on petroleum coke consumption or 

carbide production, calcium carbide used in the production of acetylene used in welding applications, and default 

emission factors. Where AD on petroleum coke consumption are used the CCF and COF of the petroleum coke 

can be obtained from Volume 2, Chapter 1 and the result must be multiplied by 44/12 to convert C to CO2. The 

basic equation for estimating emissions is: 

EQUATION 3.11 

EMISSIONS FROM CARBIDE PRODUCTION

ECO2 = AD • EF

Where: 

ECO2 = emissions of CO2, tonnes 

AD = activity data on petroleum coke consumption or carbide production, tonnes raw material used or 

tonnes carbide produced 

EF = CO2 emission factor. There are two options as follows: 

When carbide production is used as activity data, EF should be average CO2 emissions per unit of 

output for carbide production, tonnes CO2/tonne carbide production. 

When petroleum coke consumption is used as activity data, EF should be CCF (carbon content 
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3.42 2006 IPCC Guidelines for National Greenhouse Gas Inventories 

factor) multiplied by COF (carbon oxidation factor) multiplied by 44/12 and adjusted to account for 

the C contained in the product, tonnes CO2/tonne material used 

Adjustment factor for SiC = 0.35 ⇒ Emission factor = 0.65 • CCF • COF • 44/12; 

Adjustment factor for CaC2 = 0.67 ⇒ Emission factor = 0.33 • CCF • COF • 44/12. 

Equation 3.11 can also be used to estimate CH4 emissions, where EF is the appropriate emission factor for CH4. 

Estimation of emissions from CaC2 needs to include emissions of CO2 indirectly attributable to CaC2 that is used 

in acetylene production. Equation 3.11 can be applied where AD is the amount of CaC2 used and EF is the 

emission factor associated with this use. Under the Tier 1 method it is good practice to assume that all CaC2 used 

in acetylene production gives rise to CO2 emissions. 

Tier 2 method 

The Tier 2 method uses plant-level data on production of carbide and the amount of C contained in the product. 

For CaC2, data on the use of CaC2 for the production of acetylene used in welding applications is also required. 

Emissions from production and use can be estimated with Equation 3.11 using default emission factors. Where 

acetylene is produced from CaC2 at another location and the quantity of CaC2 used for this purpose is not known, 

it is good practice to document this fact. 

Tier 3 method 

The Tier 3 method requires plant-level data on the petroleum coke input along with the CCF and COF if 

available; alternatively, country specific Energy Sector values for CCF and COF may be used. Plant-level data 

on the amount of C contained in the product are also required. 

In the case of CaC2, data on the use of CaC2 for the production of acetylene used in welding applications are 

required, as are plant-level emission factors. Where acetylene is produced from CaC2 at another location and the 

quantity of CaC2 used for this purpose is not known, it is good practice to document this fact. In addition, plantlevel emission factors for CH4 need to be collected. Equation 3.11 can be applied to estimate emissions for each 

plant and total national emissions are the sum of these estimates. 

Production data are not used in the calculation but should be collected for reporting purposes. Where acetylene 

production data cannot be disaggregated by use, national inventory compilers using the Tier 3 method are 

encouraged to account for any emissions at the point where they arise; for example, emissions from acetylene 

use in welding applications should be accounted for at the point of use of acetylene using a country specific 

emission factor. A similar approach should be followed for other uses of acetylene. 
Chapter 3: Chemical Industry Emissions 

2006 IPCC Guidelines for National Greenhouse Gas Inventories 3.43 

Figure 3.5 Decision tree for estimation of CO2 and CH4 emissions from carbide 

production 

Start

Are

plant-level

data available on the 

petroleum coke

input1

?

Is this a key

category2

?

Are

plant-level carbide

production data

available?

Yes

No

No

Collect data for the Tier 3

or Tier 2 method.

Use the plant-specific coke consumption

data including C content and percent 

oxidised, along with plant-specific

CH4 emission factor as basis for the

Tier 3 method.

Calculate emissions using plant-level

data on production of carbide and plantspecific emission factors. For the plants 

where plant-specific emission factors are

not available, use default emission factors.

Use national aggregate input data, national 

production data or production capacity data 

and default emission factors to calculate 

emissions.

Box 1: Tier 1

Box 2: Tier 2

Box 3: Tier 3

Note:

1. "Input data" means raw material consumption data.

2. See Volume 1 Chapter 4, Methodological Choice and Identification of Key Categories (noting Section 4.1.2 on limited resources), for 

discussion of key categories and use of decision trees.

No

Yes

Yes

3.6.2.2 CHOICE OF EMISSION FACTORS

Tier 1 method 

The Tier 1 method uses default values for CCF, COF and C contained in the product where petroleum coke is 

used in the estimation. Alternatively, where carbide production is used, the method uses default emission factors 

shown in Tables 3.7 and 3.8 where relevant. In both cases, the default factor for CaC2 use is applied. 

Tier 2 method 

As for the Tier 1 method, the Tier 2 method uses default emission factor values except for the amount of C 

contained in the product, where plant-level data are required. 

Tier 3 method 

The Tier 3 method requires plant-level data for all variables except for CCF and COF of the petroleum coke 

where country specific Energy Sector values may be used. This includes plant-level emission factors for lime if 

it is produced in-house and plant-level emission factors for CaC2 used to produce acetylene for welding 

applications. 
Volume 3: Industrial Processes and Product Use 

3.44 2006 IPCC Guidelines for National Greenhouse Gas Inventories 

CO2 from silicon carbide production 

More carbon is needed in the silicon carbide production process than calculated from a stoichiometric reaction. 

The excess carbon is oxidised during the process, little is left as ash (Raaness, 1991). Typical default values for 

Norwegian plants for carbon content in coke are 97 percent and for carbon contained in product, 35 percent. This 

implies a typical emission factor of 2.3 tonnes CO2/tonne petroleum coke used (IPCC, 1997), or 2.62 tonnes 

CO2/tonne carbide produced. 

CH4 from silicon carbide production 

Measurements at Norwegian plants suggest emission factors of 10.2 kg CH4/tonne petroleum coke or 11.6 kg 

CH4/tonne carbide produced (IPCC, 1997). 

TABLE 3.7 

DEFAULT FACTORS FOR CO2 AND CH4 EMISSIONS FROM SILICON CARBIDE PRODUCTION

Process Emission Factor 

(tonnes CO2/tonne 

raw material used) 

Emission Factor 

(kg CH4/tonne raw 

material used) 

Emission Factor 

(tonnes CO2/tonne 

carbide produced) 

Emission Factor 

(kg CH4/tonne 

carbide produced) 

Silicon carbide 

production 2.30 10.2 2.62 11.6 

Source: Revised 1996 IPCC National Greenhouse Gas Inventories, Vol.3, p.2.21 (IPCC, 1997) 

CO2 from calcium carbide production 

Emission factors may be derived from the use of raw materials (petroleum coke) and from carbide production 

using a mass-balance approach. Limestone used in carbide manufacture contains about 98 percent CaCO3 and is 

accounted for elsewhere. 1 750 kg limestone (or 950 kg CaO), 640 kg of petroleum coke and 20 kg carbon 

electrodes are required to produce 1 tonne of carbide. 

The default emission factors for estimating emissions are included in Table 3.8. 

TABLE 3.8 

EMISSION FACTORS FOR CO2 EMISSION FROM CALCIUM CARBIDE PRODUCTION AND USE

Process Default Emission Factor 

(tonnes CO2/tonne raw material used) 

Default Emission Factor 

(tonnes CO2/tonne carbide produced) 

Petroleum coke use 1.70 1.090 

Use of product not relevant 1.100 

Source: Revised 1996 IPCC National Greenhouse Gas Inventories, Vol.3, p.2.22 (IPCC, 1997) 

The theoretical emission factor calculated from a stoichiometric reaction is lower for the petroleum coke step 

than that shown in the table. Excess carbon is oxidised in the process and the suggested emission factors were 

calculated from the actual use of raw materials in a Norwegian plant. The emission factor for acetylene use is 

calculated from the actual (not stoichiometric) carbon content of carbide. 

The CO2 emissions may be lowered by utilising the gas when producing dicyanodiamide from carbide (Olsen, 

1991). 

3.6.2.3 CHOICE OF ACTIVITY DATA

Tier 1 method 

The Tier 1 method requires data on petroleum coke used in carbide production or national production of carbide. 

These data may be obtained from national statistics or from industrial and trade organizations representing 

carbide and petroleum coke producers. 

Tier 2 method 

Activity data required for the Tier 2 method comprise plant-level data on carbide produced and the amount of 

CaC2 used in the production of acetylene for welding applications. 
Chapter 3: Chemical Industry Emissions 

2006 IPCC Guidelines for National Greenhouse Gas Inventories 3.45 

Tier 3 method 

The Tier 3 method requires plant-level activity data for all variables including the petroleum coke input and 

CaC2 used to produce acetylene for welding applications. 

The Tier 2 methods require the collection of activity data from individual plants or companies. In Tier 1 the 

activity data provided by national statistics or by industrial and trade organizations associated with carbide and 

petroleum coke production should be used. However, if sufficient plant-specific or company-specific data are 

available, they may be used to estimate emissions. 

3.6.2.4 COMPLETENESS

Carbide production plants are generally known in each country. As a result, carbide production data may be 

available in national statistical databases, or could be collected, even if these data have not been published in 

national statistics. The petroleum coke consumption data may be obtained directly from carbide production 

plants, or from coke producers and traders. Activity data and emissions estimation is complicated by the fact that 

acetylene produced from CaC2 is not necessarily produced at the same plant that produces the CaC2. This needs 

to be accounted for when using the higher tier methods, with emissions originating from the use of CaC2

accounted at the point where the emissions occur; for example, in the case of acetylene used in welding 

applications, where the acetylene is produced at a different location to the CaC2 emissions should be accounted 

for at the point of production of the acetylene on the assumption that it will be used in a short time after 

production. 

Application of the Tier 2 and 3 methods assumes the bottom-up (plant by plant) estimation of emissions and 

plant-level data collection. In countries where only a subset of plants report data for the Tier 3 method or where 

there is a transition from Tier 2 to Tier 3, it may not be possible to report emissions using Tier 3 for all facilities 

during the transition. Where data for the Tier 3 method are not available for all plants, Tier 2 could be used for 

the remaining plants. Also, where data for the Tier 2 method are reported by only a subset of plants or where 

there is a transition from Tier 1 to Tier 2, it may be possible to determine the share of production represented by 

non-reporting plants and use this information to estimate the remaining emissions using Tier 1 in order to ensure 

completeness during the transition period. 

3.6.2.5 DEVELOPING A CONSISTENT TIME SERIES

It is good practice to estimate emissions from carbide production using the same method for every year in the 

time series. Where data are unavailable to support a more rigorous method for all years in the time series, it is 

good practice is to recalculate these gaps according to the guidance provided in Volume 1, Chapter 5. 

3.6.3 Uncertainty assessment 

3.6.3.1 EMISSION FACTOR UNCERTAINTIES

In general, the default CO2 emission factors are relatively uncertain because industrial-scale carbide production 

processes differ from the stoichiometry of theoretical chemical reactions. The uncertainty in the emission factors 

for CH4 is due to the possible variations in the hydrogen-containing volatile compounds in the raw material 

(petroleum coke) that are used by different manufacturers and due to the possible variations in production 

process parameters. Where uncertainty values are not available from other sources, a default value of ±10 

percent can be used. 

It is good practice to obtain uncertainty estimates at the plant level which should be lower than uncertainties 

associated with default values. 

3.6.3.2 ACTIVITY DATA UNCERTAINTIES

Where activity data are obtained directly from plants, uncertainty estimates can be obtained from producers. This 

will include uncertainty estimates for petroleum coke and limestone used and for carbide production data. Data 

that are obtained from national statistical agencies or from industrial and trade organizations usually do not 

include uncertainty estimates. It is good practice to consult with national statistical agencies to obtain 

information on any sampling errors. Where national statistic agencies collect carbide production data from 

production facilities, uncertainties in national statistics are not expected to differ from uncertainties estimated 
Volume 3: Industrial Processes and Product Use 

3.46 2006 IPCC Guidelines for National Greenhouse Gas Inventories 

from plant-level consultations. Where uncertainty values are not available from other sources, a default value of 

±5 percent can be used. 

3.6.4 Quality Assurance/Quality Control (QA/QC), 

Reporting and Documentation 

3.6.4.1 QUALITY ASSURANCE/QUALITY CONTROL

It is good practice to conduct quality control checks as outlined in Volume 1, Chapter 6, and an expert review of 

the emission estimates. More extensive quality control checks and quality assurance procedures may be 

applicable, particularly if higher tier methods are used to determine emissions from this source category. 

Inventory compilers are encouraged to use higher tier QA/QC for key categories as identified in Volume 1, 

Chapter 4. 

In addition to the guidance given in Volume 1, specific procedures of relevance to this source category are 

outlined below. 

Comparison of emission estimates using different approaches 

If the Tier 2 (plant-specific) method is used, then inventory compilers should compare the emission estimates to 

the estimates calculated using national level activity data (Tier 1). The inventory compilers are also encouraged 

to compare the emission estimates calculated using different modifications of the same methods. 

The results of such comparison should be recorded for internal documentation, including explanation for any 

discrepancies. 

Review of emission factors 

Inventory compilers should compare aggregated national emission factors with the IPCC default emission factors 

in order to determine if the national factor is reasonable relative to the IPCC default. The same procedure (i.e., 

comparison with the IPCC default) should be applied to plant specific emission factors. Differences between 

national or plant specific factors and default factors should be explained and documented, particularly if they are 

representative of different circumstances. 

Plant-specific data check 

For plant-specific data, inventory compilers should review inconsistencies between plants to establish whether 

they reflect errors, different measurement techniques, or result from real differences in raw materials, operational 

conditions or technology. 

Inventory compilers should ensure that activity data and emission factors are developed in accordance with 

internationally recognized and proven measurement methods. If any emission measurements from individual 

plants are collected inventory compilers should ensure that the measurements were made according to the 

recognised national or international standards. If the measurement practices fall this criterion, then the use of this 

emission factors and activity data should be carefully evaluated, uncertainty estimations reconsidered and 

qualifications documented. 

Expert review 

Inventory compilers are encouraged to include key industrial and trade organizations associated with carbide and 

petroleum coke production in a review process. This process should begin on the early stage of the inventory 

development to provide input to the development and review of methods and data acquisition. 

Third party reviews may be also useful for this source category, particularly in relation of initial data collection, 

transcription, calculation and documentation. 

3.6.4.2 REPORTING AND DOCUMENTATION

It is good practice to document and archive all information required to produce the national emissions inventory 

estimates as outlined in Volume 1, Section 6.11. Recalculation of previous years emissions also should be 

documented and archived. 
Chapter 3: Chemical Industry Emissions 

2006 IPCC Guidelines for National Greenhouse Gas Inventories 3.47 

3.7 TITANIUM DIOXIDE PRODUCTION 

3.7.1 Introduction 

Titanium dioxide (TiO2) is one of the most commonly used white pigments. The main use is in paint 

manufacture followed by paper, plastics, rubber, ceramics, fabrics, floor covering, printing ink, and other 

miscellaneous uses (Austin, 1984; Lowenheim and Moran, 1975). Given production of around 4 million tonnes 

of TiO2, and the substantial use of the chloride route, carbon dioxide (CO2) emissions are likely to be significant 

and need to be accounted for in greenhouse gas inventories. Global production by the chloride route has increase 

approximately eight fold since 1970 whilst sulphate route production has been relatively stable (Kirk-Othmer, 

1999; p. 2017). Note that in the discussion, titanium dioxide products are referred to generically as titanium 

dioxide unless there is a need to make a distinction between the products. The discussion applies to titanium slag, 

synthetic rutile (>90 percent TiO2) and rutile TiO2. 

3.7.2 Methodological issues 

TiO2 is produced as anatase TiO2 and rutile TiO2. The forms of TiO2 differ in terms of the crystalline structure 

and purity of the final product. Anatase TiO2 may be produced by digesting ilmenite (essentially ferrous titanate 

(FeO.TiO2)) with sulphuric acid, the sulphate process, or from titanium slag. Basic reaction equations for the 

acid digestion route are (Lowenheim and Moran, 1975; p. 814): 

FeTiO3 + 2H2SO4 → FeSO4 + TiO.SO4 + 2H2O 

TiO.SO4 + 2H2O → TiO2.H2O + H2SO4

TiO2.H2O + heat → TiO2 + H2O 

The sulphate route process does not give rise to process greenhouse gas emissions that are of significance. 

There are three processes that are used in the production of TiO2 that lead to process greenhouse gas emissions: 

titanium slag production in electric furnaces, synthetic rutile production using the Becher process, and rutile 

TiO2 production via the chloride route. 

Titanium slag used for production of anatase TiO2 is produced from electric furnace smelting of ilmenite. Where 

titanium slag is used the acid reduction step is not required as the electric furnace smelting reduces the ferric iron 

contained as an impurity in ilmenite. Rutile TiO2 may be produced by further processing of the anatase TiO2. 

Process emissions arise from the reductant used in the process. 

Production of synthetic rutile can give rise to CO2 emissions where the Becher process is used. This process 

reduces the iron oxide in ilmenite to metallic iron and then reoxidises it to iron oxide, and in the process 

separates out the titanium dioxide as synthetic rutile of about 91 to 93 percent purity (Chemlink, 1997). Black 

coal is used as the reductant and the CO2 emissions arising should be treated as industrial process emissions. 

The main route for the production of rutile TiO2 is the chloride route. Rutile TiO2 is produced through the 

carbothermal chlorination of rutile ore or synthetic rutile to produce titanium tetrachloride (TiCl4) and oxidation 

of the TiCl4 vapours to TiO2 according to the following reactions (Kirk-Othmer, 1999; p.2017): 

2TiO2 + 4Cl2 + 3C → 2TiCl4 + 2CO + CO2

TiCl4 + O2 → TiO2 + 2Cl2

Based on stoichiometry and assuming complete conversion of the input C to CO2 through further conversion of 

CO in excess air, the CO2 emission factor cannot be less than 0.826 tonnes of CO2 per tonne of TiO2 (based on 

1.5 moles of CO2 per mole of TiO2). 

3.7.2.1 CHOICE OF METHOD

The general approach for calculating CO2 emissions from titanium dioxide production is the same irrespective of 

the product because the emissions are based on the quantity of reducing agent or carbothermal input. The choice 

of a good practice method depends on national circumstances as shown in the decision tree in Figure 3.6. 

Process emissions of carbon dioxide in TiO2 production take place primarily as a result of anode carbon 

oxidisation in the production of titanium slag, coal oxidisation in the process of producing synthetic rutile using 

the Becher process, and petroleum coke oxidisation in the process of producing rutile TiO2 via the chloride route. 

Methods are classified according to the extent of plant-level data that are available. 
Volume 3: Industrial Processes and Product Use 

3.48 2006 IPCC Guidelines for National Greenhouse Gas Inventories 

TIER 1 METHOD 

The Tier 1 method uses a default emission factor per unit of output multiplied by activity data obtained from 

national statistics. The basic equation for estimating CO2 emissions is: 

EQUATION 3.12 

CO2 EMISSIONS FROM TITANIUM SLAG, SYNTHETIC RUTILE AND RUTILE TIO2 PRODUCTION –

TIER 1 

= ∑( • )

i

ECO2 ADi EFi

Where: 

ECO2 = emissions of CO2, tonnes 

ADi = production of titanium slag, synthetic rutile or rutile TiO2 (product i), tonnes 

EFi = CO2 emissions per unit of production of titanium slag, synthetic rutile or rutile TiO2 (product i), 

tonnes CO2/tonne product 

TIER 2 METHOD 

Emissions can be calculated from the consumption of the reducing agent for electrode carbon (titanium slag), 

and coal (synthetic rutile) in the Becher process, and the carbothermal input (petroleum coke) for rutile TiO2

from the chloride rout process. The Tier 2 method uses plant-level data on the quantities of reducing agent and 

carbothermal input to derive emissions as follows: 

EQUATION 3.13 

CO2 EMISSIONS FROM TITANIUM SLAG, SYNTHETIC RUTILE AND RUTILE TIO2 PRODUCTION –

TIER 2 

= ∑( • • • )

i

ECO ADi CCFi COFi 44 12 2

Where: 

ECO2 = emissions of CO2, kg 

ADi = amount of reducing agent or carbothermal input i, GJ 

CCFi = carbon content factor of reducing agent or carbothermal input i, kg C/GJ 

COFi = carbon oxidation factor for reducing agent or carbothermal input i, fraction 

To achieve the highest accuracy, good practice is to apply Equation 3.13 at the plant-level with all data inputs 

obtained from plant operators. 

Where plant-level information is not available, good practice provides default CO2 emission factors for synthetic 

rutile and rutile TiO2 as shown in Table 3.9. A default factor for titanium slag is not available because of the 

small number of plants. 

BOX 3.6 

DOUBLE COUNTING

In order to avoid double counting, the quantities of electrode carbon, coal used as a reductant, and 

petroleum coke used in the chloride route process, must be subtracted from the quantity reported 

under energy and non-energy use in the Energy Sector. 

3.7.2.2 CHOICE OF EMISSION FACTORS

TIER 1 METHOD 

If plant-level information is not available, it is good practice to use default factors. These default values often 

represent midpoint or mean values of data sets (as determined by expert analysis). The extent to which they 

represent a specific plant’s emission rate is unknown. Default factors by product are provided in Table 3.9, and 

should be used only in cases where plant-specific data are not available. The default factors are based on 
Chapter 3: Chemical Industry Emissions 

2006 IPCC Guidelines for National Greenhouse Gas Inventories 3.49 

estimates of reductant or carbothermal input per unit of output assuming complete conversion of the C content to 

CO2. 

TIER 2 METHOD 

Plant-level data provides the most rigorous data for calculating CO2 emissions from titanium dioxide production. 

For the Tier 3 method, C content of the reductant and carbothermal inputs along with the proportion of C 

oxidised are the key emission factor variables for deriving the quantity of CO2 emitted. 

TABLE 3.9 

DEFAULT FACTORS FOR TITANIUM DIOXIDE PRODUCTION (TONNES CO2 PER TONNE PRODUCT) 

Product Emission factor and respective uncertainty 

(tonnes CO2/tonne product) 

Titanium slag1 Not available 

Synthetic rutile2 1.43 (± 10%) 

Rutile titanium dioxide (chloride route)3 1.34 (± 15%) 

Source: 

1

 A default emission factor is not available because there are two plants only, Richards Bay in South Africa, and Allard 

Lake in Canada, and data are confidential. It is good practice for the respective countries to include plant specific 

estimates of emissions in their national greenhouse gas inventories. 

2

 Derived from data provided by Iluka Resources. 

3

 Adapted from EIPPCB (2004a; p.99). 

Figure 3.6 Decision tree for estimation of CO2 emissions from titanium dioxide 

production 

Start

Are

plant-level data on

the quantities of reducing agent 

and carbothermal

input available?

Are

national

aggregate data on

production of titanium slag,

synthetic rutile or rutile

TiO2 available?

Is this a key

category1

?

Yes

Yes

No

Collect data for

the Tier 2 method.

Use the plant-level data on the

quantities of reducing agent

and carbothermal input, and

carbon content and carbon

oxidation factors.

Calculate emissions using

national aggregate data on

production of titanium slag,

synthetic rutile or rutile TiO2

and default emission factors.

Box 1: Tier 1

Box 2: Tier 2

Note:

1. See Volume 1 Chapter 4, Methodological Choice and Identification of Key Categories (noting Section 4.1.2 on limited resources), for 

discussion of key categories and use of decision trees.

No

Yes

No

Gather production data or

use production capacity data.
Volume 3: Industrial Processes and Product Use 

3.50 2006 IPCC Guidelines for National Greenhouse Gas Inventories 

3.7.2.3 CHOICE OF ACTIVITY DATA

It is good practice to compile activity data at a level of detail that allows the use of the Tier 2 method. When 

applying the methods it is essential that a clear distinction is made between the products to avoid multiplying the 

incorrect emission factor by activity data. 

TIER 1 METHOD 

The Tier 1 method requires data on national production of titanium slag, synthetic rutile and rutile TiO2. If 

national-level activity data are not available, information on production capacity can be used with emissions 

estimated using a default emission factor. It is good practice to multiply the total national production capacity by 

a capacity utilisation factor of 80 percent ± 10 percent (i.e., a range of 70-90 percent). 

TIER 2 METHOD 

The plant-level activity data required for the Tier 2 method are total reductant use, total carbon electrode 

consumption, and total carbothermal input. It is good practice to also collect data on total titanium slag 

production, total synthetic rutile production, and total rutile TiO2 production. Collection of production data 

enables comparisons of inputs per unit of outputs over time and provides a sound basis for ensuring time series 

consistency. Where plant-level emission factors are used, good practice is to collect plant-level production data. 

Typical plant-level activity data is assumed to be accurate to ±2 percent due to the economic value of having 

accurate information. If plant-level data are not available, nationally compiled production data may be used. 

3.7.2.4 COMPLETENESS

Complete coverage for titanium dioxide production requires accounting for all emissions from all sources 

including titanium slag, synthetic rutile and rutile TiO2. CO2 emissions are the main process emissions. In order 

to include emissions of NOx, CO and SO2 from this source category, see guidance provided in Chapter 7 of 

Volume 1: General Guidance and Reporting. 

3.7.2.5 DEVELOPING A CONSISTENT TIME SERIES

CO2 emissions should be recalculated for all years whenever emission calculation methods are changed (e.g., if 

the inventory compiler changes from the use of default values to actual values determined at the plant level). If 

plant-specific data are not available, including plant-specific production data, for all years in the time series, it 

will be necessary to consider how current plant data can be used to recalculate emissions for previous years. It 

may be possible to apply current plant-specific emission factors to production data from previous years, provided 

that plant operations have not changed substantially. Recalculation is required to ensure that any changes in 

emissions trends are real and not an artefact of changes in procedure. It is good practice to recalculate the time 

series according to the guidance provided in Volume 1, Chapter 5. 

3.7.3 Uncertainty assessment 

3.7.3.1 EMISSION FACTOR UNCERTAINTIES

Uncertainties for the default values are estimates based on expert judgement. It is good practice to obtain 

uncertainty estimates at the plant level which should be lower than uncertainty values associated with default 

values. 

3.7.3.2 ACTIVITY DATA UNCERTAINTIES

Where activity data are obtained from plants, uncertainty estimates can be obtained from producers. This will 

include uncertainty estimates for reductant use, carbothermal inputs, and production data. Data that are obtained 

from national statistical agencies usually do not include uncertainty estimates. It is good practice to consult with 

national statistical agencies to obtain information on any sampling errors. Where national statistical agencies 

collect data from the population of titanium dioxide production facilities, uncertainties in national statistics are 

not expected to differ from uncertainties established from plant-level consultations. Where uncertainty values are 

not available from other sources, a default value of ±5 percent can be used. 
Chapter 3: Chemical Industry Emissions 

2006 IPCC Guidelines for National Greenhouse Gas Inventories 3.51 

3.7.4 Quality Assurance/Quality Control (QA/QC), 

Reporting and Documentation 

3.7.4.1 QUALITY ASSURANCE/QUALITY CONTROL

It is good practice to conduct quality control checks as outlined in Volume 1, Chapter 6. More extensive quality 

control checks and quality assurance procedures are applicable, if higher tier methods are used to determine 

emissions. Inventory compilers are encouraged to use higher tier QA/QC for key categories as identified in 

Volume 1, Chapter 4. 

Comparison of emission factors 

Inventory compilers should check if the estimated emission factors are within the range of default emission 

factors provided for the Tier 1 method, and also ensure that the emission factors are consistent with the values 

derived from analysis of the process chemistry. For example, the CO2 generation rate for rutile TiO2 from the 

chloride route process should not be less than 0.826 tonnes of CO2 per tonne of rutile TiO2 produced. If the 

emission factors are outside of the estimated ranges, it is good practice to assess and document the plant-specific 

conditions that account for the differences. 

If emission measurements from individual plants are collected, inventory compilers should ensure that the 

measurements were made according to recognised national or international standards. QC procedures in use at 

the site should be directly referenced and included in the QC plan. If the measurement practices were not 

consistent with QC standards, the inventory compiler should reconsider the use of these data. 

3.7.4.2 REPORTING AND DOCUMENTATION

It is good practice to document and archive all information required to produce the national emissions inventory 

estimates as outlined in Volume 1, Section 6.11. It is not practical to include all documentation in the national 

inventory report. However, the inventory should include summaries of methods used and references to source 

data such that the reported emissions estimates are transparent and steps in their calculation may be retraced. 

Plant-specific data check 

The following plant-specific data is required for adequate auditing of emissions estimates: 

• Activity data comprising electrode carbon consumption (titanium slag), coal reductant use (synthetic rutile), 

carbothermal input (rutile TiO2), titanium slag production, synthetic rutile production, and rutile TiO2

production; 

• Emission factor data including the carbon content of the reductant (carbon electrode and coal) and 

carbothermal input (petroleum coke), and the proportion oxidised in the process; 

• Calculations and estimation method; 

• List of assumptions; 

• Documentation of any plant-specific measurement method, and measurement results. 

In general production and process data are considered proprietary by operators, especially where there are only a 

small number of plants within a country. It is good practice to apply appropriate techniques, including 

aggregation of data, to ensure protection of confidential data. 
Volume 3: Industrial Processes and Product Use 

3.52 2006 IPCC Guidelines for National Greenhouse Gas Inventories 

3.8 SODA ASH PRODUCTION 

3.8.1 Introduction 

Soda ash (sodium carbonate, Na2CO3) is a white crystalline solid that is used as a raw material in a large number 

of industries including glass manufacture, soap and detergents, pulp and paper production and water treatment. 

Carbon dioxide (CO2) is emitted from the use of soda ash and these emissions are accounted for as a source 

under the relevant using industry as discussed in Volume 3, Chapter 2. CO2 is also emitted during production 

with the quantity emitted dependent on the industrial process used to manufacture soda ash. 

Emissions of CO2 from the production of soda ash vary substantially with the manufacturing process. Four 

different processes may be used commercially to produce soda ash. Three of these processes, monohydrate, 

sodium sesquicarbonate (trona) and direct carbonation, are referred to as natural processes. The fourth, the 

Solvay process, is classified as a synthetic process. Calcium carbonate (limestone) is used as a source of CO2 in 

the Solvay process. Other uses of limestone and other carbonates are discussed in Volume 3, Chapter 2. 

3.8.2 Natural soda ash production 

About 25 percent of the world production is produced from natural sodium carbonate-bearing deposits referred 

to as natural processes. During the production process, Trona (the principal ore from which natural soda ash is 

made) is calcined in a rotary kiln and chemically transformed into a crude soda ash. Carbon dioxide and water 

are generated as by-products of this process. Carbon dioxide emissions can be estimated based on the following 

chemical reaction: 

2Na2CO3.NaHCO3.2H2O (Trona) → 3Na2CO3 (Soda Ash) + 5H2O + CO2

3.8.2.1 METHODOLOGICAL ISSUES

CHOICE OF METHOD 

The choice of method will depend on national circumstances. Emissions can be estimated using an output-based 

approach (emissions per unit of output), or an input-based approach (emissions per unit of input). However, it is 

good practice to use the input-based method where data are available. 

Methods are classified according to the extent of plant-level data that are available. The Tier 1 method is based 

on default values and national statistics, and the Tier 2 method is based on complete plant-level input or output 

data and plant specific emission factors. If there is monitoring and direct measurement of CO2 emissions this 

would be equivalent to a Tier 3 method. 

Tier 1 method 

Natural soda ash production emits CO2 through the thermal decomposition (calcination) of the Trona 

(Na2CO3.NaHCO3.2H2O) to produce soda ash. According to the chemical reaction presented above, it takes 

10.27 tonnes of Trona to produce 1 tonne of carbon dioxide. Hence, for natural soda ash production using Trona, 

emissions of carbon dioxide can be calculated from the Trona input or natural soda ash output by the following 

formula: 

EQUATION 3.14 

CO2 EMISSIONS FROM NATURAL SODA ASH PRODUCTION – TIER 1 

ECO2 = AD • EF

Where: 

ECO2 = emissions of CO2, tonnes 

AD = quantity of Trona used or soda ash produced, tonnes of Trona used or tonnes natural soda ash 

produced 

EF = emission factor per unit of Trona input or natural soda ash output, tonnes CO2/tonne of Trona or 

tonnes CO2/tonne natural soda ash produced: EFTrona = 0.097 tonnes CO2/tonne of Trona, EFSoda Ash = 

0.138 tonnes CO2/tonnes natural soda ash produced. 
Chapter 3: Chemical Industry Emissions 

2006 IPCC Guidelines for National Greenhouse Gas Inventories 3.53 

It is good practice to assess the available national statistics for completeness. The choice of good practice

methods depends on national circumstances, as shown in Figure 3.7: Decision Tree for Estimation of CO2

Emissions from Natural Soda Ash Production. If no data are available for the purity of the Trona input, it is good 

practice to assume it is 90 percent and adjust the emission factor shown in Equation 3.14. 

Tier 2 method 

To use the Tier 2 method, it is necessary to gather complete data on Trona consumption or natural soda ash 

production for each of the plants within the country along with plant-specific emission factors for the Trona 

input or soda ash output. The CO2 emissions for each plant can be calculated using either variation of Equation 

3.14. For plants where plant-specific emission factors are not available, the default emission factors provided in 

Equation 3.14 can be used. Total CO2 emissions are the sum of the emissions from all plants. 

Tier 3 method 

The Tier 3 method uses plant-level CO2 emissions data obtained from direct measurement. Total emissions are 

the sum of emissions from all plants. 

Figure 3.7 Decision tree for estimation of CO2 emissions from natural soda ash 

production 

Start

Are

plant-level CO2

emissions data obtainable from 

direct measurement?

Are

plant-level data on

Trona consumption

available?

Are

plant-level

data on natural soda ash 

production

available?

No

No

Collect data for the No

Tier 3 or 2 method.

Use plant-level CO2 

emissions data obtained

from direct measurement.

Calculate emissions using

plant-level natural soda

ash production data and

plant-specific emission

factors, if available.

Box 2: Tier 2

Box 4: Tier 3

Note:

1. See Volume 1 Chapter 4, Methodological Choice and Identification of Key Categories (noting Section 4.1.2 on limited resources), for 

discussion of key categories and use of decision trees.

Yes

Yes

No Is this a key

category1

?

Calculate emissions

using plant-level Trona 

consumption data, using 

plant-specific emission

factor if available.

Calculate emissions using national aggregate data 

of Trona consumption or natural soda ash 

production and default emission factor. In case 

the national aggregate data are not available, 

estimate it by using production capacity data.

Box 3: Tier 2

Box 1: Tier 1

Yes

Yes
Volume 3: Industrial Processes and Product Use 

3.54 2006 IPCC Guidelines for National Greenhouse Gas Inventories 

CHOICE OF EMISSION FACTORS 

Tier 1 method 

The Tier method uses the default emission factors presented in Equation 3.14. The default emission factors are 

derived from the stoichiometric ratio between soda ash produced and purified sodium sesquicarbonate obtained 

from Trona. They are based on the main natural production process that is used at present, where soda ash is 

produced by calcination of purified sodium sesquicarbonate. 

Tier 2 method 

The Tier 2 method requires plant-level emission factors per unit of Trona input or per unit of natural soda ash 

output. Plant-level emission factors should reflect the fractional purities of the Trona input and natural soda ash 

output and it is good practice to ensure that these are taken into account in the derivation of plant-level emission 

factors. 

CHOICE OF ACTIVITY DATA 

It is good practice to compile activity data at a level of detail that allows the use of the Tier 2 method. When 

applying the methods it is essential that a clear distinction is made between the products to avoid multiplying the 

incorrect emission factor by activity data. 

Tier 1 method 

The Tier 1 method requires data on national consumption of Trona or national production of natural soda ash. If 

national-level activity data are not available, information on production capacity can be used with emissions 

estimated using a default emission factor. It is good practice to multiply the total national production capacity by 

a capacity utilisation factor of 80 percent ± 10 percent (i.e., a range of 70-90 percent). 

Tier 2 method 

Activity data should be collected at the plant-level to use the Tier 2 method. The most important data are the 

amount of Trona used for soda ash production and the amount of natural soda ash produced at each plant.

Although soda ash production is not used in the calculation if emissions are derived from Trona input, it is good 

practice to collect and report these data to enable comparisons of inputs per unit of outputs over time and 

provide a sound basis for ensuring time series consistency. 

COMPLETENESS 

Completeness of the activity data (e.g., Trona utilisation) is a crucial attribute of good practice. Therefore, it is 

good practice to assess the available national statistics for completeness. If data are available at the plant-level, 

it is good practice to aggregate these data and check the result with the data available at a national level. This 

practice enables assessment of whether any significant soda ash producer is omitted, and ensures that all 

production processes within the country have been considered. If data at the plant-level are not available, it is 

good practice to use production capacity data along with national statistics to estimate the emissions for 

completeness purposes. 

DEVELOPING A CONSISTENT TIME SERIES 

It is good practice to calculate emissions from soda ash using the same method for every year in the time series. 

Where data are unavailable to support a more rigorous method for all years in the time series, good practice is to 

recalculate these gaps according to the guidance provided in Volume 1, Chapter 5. 

3.8.2.2 UNCERTAINTY ASSESSMENT

EMISSION FACTOR UNCERTAINTIES 

The stoichiometric ratio is an exact number and assuming 100 percent purity of the input or output, the 

uncertainty of the default emission factor is negligible. However, the default factors do not take into account the 

fractional purities of either the Trona input or soda ash output and, in both cases, are expected to result in 

consistent over-estimation of emissions. As noted earlier, if no data are available for the purity of the Trona 

input, it is good practice to assume it is 90 percent and adjust the emission factor shown in Equation 3.14. It is 

good practice to develop uncertainty estimates based on plant-level data. 

ACTIVITY DATA UNCERTAINTIES 

Where activity data are obtained from plants, uncertainty estimates can be obtained from producers. This will 

include uncertainty estimates for Trona used and natural soda ash used. Data that are obtained from national 

statistical agencies usually do not include uncertainty estimates. It is good practice to consult with national 

statistical agencies to obtain information on any sampling errors. Where national statistical agencies collect data 
Chapter 3: Chemical Industry Emissions 

2006 IPCC Guidelines for National Greenhouse Gas Inventories 3.55 

from the population of soda ash production facilities, uncertainties in national statistics are not expected to differ 

from uncertainties established from plant-level consultations. Where uncertainty values are not available from 

other sources, a default value of ±5 percent can be used. 

3.8.2.3 QUALITY ASSURANCE/QUALITY CONTROL (QA/QC),

REPORTING AND DOCUMENTATION

QUALITY ASSURANCE/QUALITY CONTROL 

It is good practice to conduct quality control checks as outlined in Volume 1, Chapter 6, and an expert review of 

the emissions estimates. Additional quality control checks as outlined in Volume 1, and quality assurance 

procedures may also be applicable, particularly if higher tier methods are used to determine emissions from this 

source category. Inventory compilers are encouraged to use higher tier QA/QC for key categories as identified in 

Volume 1, Chapter 4. 

Comparison of the emissions estimates using different approaches 

If the bottom-up approach is used, then inventory compilers should compare the emissions estimates to the 

estimate calculated using the top-down approach. The results of such comparisons should be recorded for 

internal documentation, including explanations for any discrepancies. 

REPORTING AND DOCUMENTATION 

It is good practice to document and archive all information required to produce the national emissions inventory 

estimates as outlined in Volume1, Section 6.11. It is not practical to include all documentation in the national 

inventory report. However, the inventory should include summaries of methods used and references to data 

sources, and all the information needed to reproduce the estimate. 

Besides the emissions, good practice is to report the activity data used in the calculation (Trona utilisation) and 

the corresponding emission factors along with all assumptions used in the derivation. 

To preserve an internally consistent emission time series, whenever national methods change, good practice is to 

recalculate the entire time series. If confidentiality is an issue for any type of production, estimates may be 

aggregated to the minimum extent possible to maintain confidentiality. 

In addition, inventory compilers should document the QA/QC procedures. 

3.8.3 Solvay soda ash production 

About 75 percent of the world production of soda ash is synthetic ash made from sodium chloride. In the Solvay 

process, sodium chloride brine, limestone, metallurgical coke and ammonia are the raw materials used in a series 

of reactions leading to the production of soda ash. Ammonia, however, is recycled and only a small amount is 

lost. The series of reactions involved in the Solvay process may be described as follows: 

CaCO3 + heat → CaO + CO2 

CaO + H2O → Ca(OH)2

2NaCl + 2H2O + 2NH3 + 2CO2 → 2NaHCO3 + 2NH4Cl 

2NaHCO3 + heat → Na2CO3 + CO2 + H2O 

Ca(OH)2 + 2NH4Cl → CaCl2 + 2NH3 + 2H2O 

The net overall reaction may be summarised as:

CaCO3 + 2NaCl → Na2CO3 + CaCl2 

From the series of reactions presented above, CO2 is generated in two pyrolysis processes. The CO2 generated is 

captured, compressed and directed to Solvay precipitating towers for consumption in a mixture of brine (aqueous 

NaCl) and ammonia. Although CO2 is generated as a by-product, the CO2 is recovered and recycled for use in 

the carbonation stage and in theory the process is neutral, i.e., CO2 generation equals uptake. 

In practice, some CO2 is emitted to the atmosphere during production by the Solvay process because more CO2 is 

produced than is stoichiometrically required. The excess CO2 arises from calcining the limestone with 

metallurgical grade coke. The limestone is combined with the coke at approximately 7 percent of limestone by 

weight. 
Volume 3: Industrial Processes and Product Use 

3.56 2006 IPCC Guidelines for National Greenhouse Gas Inventories 

The estimation of the CO2 emissions from a stand alone soda ash plant should be based on an overall balance of 

CO2 around the whole chemical process. For inventory purposes, a simplified version of the balance may be used 

assuming that the CO2 emissions result from the stoichiometric oxidation of the coke carbon. The Solvay 

ammonia soda ash production process is a chemical industry activity and emissions should be reported under the 

Industrial Processes and Product Use (IPPU) Sector. 

BOX 3.7 

DOUBLE COUNTING

In order to avoid double counting, CO2 emissions generated in the process of soda ash production 

should be accounted in the IPPU Sector, and should not be included in the Energy Sector. Coke 

used in the production process should be deducted from the Energy Sector as a non-energy use of 

coke. 

3.8.3.1 QUALITY ASSURANCE/QUALITY CONTROL (QA/QC),

REPORTING AND DOCUMENTATION

The allocation of emissions from the use of metallurgical grade coke in the Solvay process to the Energy Sector

means that a methodology for estimating these emissions is not provided in the Industrial Processes and 

Product Use Sector. However, data on soda ash production from the Solvay process should be collected and 

collated to ensure that all data on soda ash production by process are available for recording, reporting, archiving 

and reconciliation with national statistics on soda ash use. 

QUALITY ASSURANCE/ QUALITY CONTROL 

It is good practice to conduct quality control checks as outlined in Volume 1, Chapter 6. Additional quality 

control checks as outlined in Volume 1, and quality assurance procedures may also be applicable. Inventory 

compilers are encouraged to use higher tier QA/QC for key categories as identified in Volume 1, Chapter 4. 

REPORTING AND DOCUMENTATION 

It is good practice to document and archive all information required to produce the national emissions inventory 

estimates as outlined in Volume1, Section 6.11. It is not practical to include all documentation in the national 

inventory report. However, the inventory should include summaries of methods used and references to data 

sources, and all the information needed to reproduce the estimate. 
Chapter 3: Chemical Industry Emissions 

2006 IPCC Guidelines for National Greenhouse Gas Inventories 3.57 

3.9 PETROCHEMICAL AND CARBON BLACK 

PRODUCTION 

3.9.1 Introduction 

The petrochemical industry uses fossil fuels (e.g., natural gas) or petroleum refinery products (e.g., naphtha) as 

feedstocks. This section provides guidance for estimating emissions from the production of methanol, ethylene 

and propylene2

, ethylene dichloride, ethylene oxide, and acrylonitrile. These petrochemicals are addressed in 

detail because their global production volume and associated greenhouse gas emissions are relatively large. 

However, the chemicals included are not intended to represent the entire petrochemical process industry. There 

are a number of other petrochemical processes that emit small amounts of greenhouse gases for which specific 

guidance is not provided (e.g., styrene production). 

This section also provides guidance for production of carbon black. Carbon black is not considered to be a 

petrochemical; however, the carbon black production process uses petrochemical feedstocks. Emissions from 

carbon black production are smaller than for petrochemical processes but may be significant for certain countries. 

Examples of feedstock to product production chains for methanol, ethylene and propylene, ethylene dichloride, 

ethylene oxide, acrylonitrile, and carbon black are included in the Annex to Section 3.9. 

Allocation and Reporting 

Within the petrochemical industry and carbon black industry, primary fossil fuels (natural gas, petroleum, coal) 

are used for non-fuel purposes in the production of petrochemicals and carbon black. The use of these primary 

fossil fuels may involve combustion of part of the hydrocarbon content for heat raising and the production of 

secondary fuels (e.g., off gases). 

Combustion emissions from fuels obtained from the feedstocks should be allocated to the source category in the 

IPPU Sector. However, where the fuels are not used within the source category but are transferred out of the 

process for combustion elsewhere (e.g., for district heating purposes) the emissions should be reported in the 

appropriate Energy Sector source category. The industries are included in the source category Chemical 

Industry (2B1 – 2B10), see Figure 1.1, Industrial Process and Product Use Source Categories in Chapter 1 of this 

volume. Further discussion of the non-energy use of fuels is included in Chapters 1 and 5 of this volume. 

Note that national energy statistics may include total combustion of fossil fuels (including natural gas, oil, and 

coal,) and also secondary fuels (such as industrial process off gases) for energy production. It is important to 

investigate if fuels used in petrochemical industries are included in national energy statistics. If this is the case, 

emissions from petrochemical processes should be subtracted from the calculated energy sector emissions to 

avoid double counting. This is particularly relevant for ethylene and methanol, where primary fuel (e.g., natural 

gas, ethane, propane) feedstock consumption may be reported in national energy statistics. 

Should carbon dioxide (CO2) capture technology be installed and used at a plant, it is good practice to deduct the 

CO2 captured in a higher tier emissions calculation. The default assumption is that there is no CO2 capture and 

storage (CCS) taking place. Any methodology taking into account CO2 capture should consider that CO2

emissions captured in the process may be both combustion and process-related. In cases where combustion and 

process emissions are to be reported separately, inventory compilers should ensure that the same quantities of 

CO2 are not double counted. In these cases the total amount of CO2 captured should preferably be reported in the 

corresponding energy combustion and IPPU source categories in proportion to the amounts of CO2 generated in 

these source categories. For additional information on CO2 capture and storage refer to Volume 3, Section 1.2.2 

and for more details on capture and storage to Volume 2, Section 2.3.4. 

Petrochemical processes may utilise CO2 captured elsewhere as a feedstock, and CO2 may also be captured from 

petrochemical processes. This may create potential double counting issues. For example, some methanol plants 

may utilise by-product CO2 captured from other industrial processes as a feedstock for methanol production. To 

avoid double counting the CO2 captured should not be reported as CO2 emissions from the process from which 

the CO2 is captured. 

 

2

 Note that there is no separate inventory methodology for propylene. Propylene is assumed to be a co-product of ethylene 

production. 
Volume 3: Industrial Processes and Product Use 

3. 58 2006 IPCC Guidelines for National Greenhouse Gas Inventories 

METHANOL 

Worldwide almost all methanol is made by way of steam reforming of natural gas. The steam reforming and shift 

reaction produce ‘synthesis gas’ comprised of CO2, carbon monoxide (CO), and hydrogen (H2). The natural gas 

to methanol production process produces methanol and by-product CO2, CO, and H2 from the synthesis gas. 

There are several alternative processes for producing methanol from natural gas or other feedstocks. These 

include conventional reforming process, combined reforming and partial oxidation process. An example of a 

feedstock to product process flow diagram for methanol production is provided in an Annex to Section 3.9

(Annex 3.9A). Process descriptions for methanol production are included in Box 3.8 below. 

BOX 3.8 

METHANOL PROCESS DESCRIPTIONS

Conventional Reforming Process

The Conventional Reforming Process for methanol production involves steam reforming (which 

may include either a single reformer unit or both a primary reformer unit and a secondary reformer 

unit) and methanol synthesis. The overall equations for the Conventional Reforming Process are: 

The surplus hydrogen from this process and methanol process purge gas containing methane (CH4) 

and non-methane volatile organic compounds (NMVOC) are recovered and burned for energy 

recovery, generally within the methanol production process, to produce process steam and/or 

electricity for the process. The Conventional Reforming Process may utilise CO2 captured from 

other industrial processes as a supplemental feedstock to the methanol production process. 

Combined Reforming Process

The Combined Reforming Process combines the Conventional Steam Reforming process with a 

Catalytic Partial Oxidation process. The Partial Oxidation chemical equations are: 

The Combined Reforming Process produces a synthesis gas that contains a more balanced ratio of 

hydrogen to carbon monoxide (CO) and CO2 than does the Conventional Reforming Process, and 

does not produce a hydrogen gas stream for energy recovery. The Combined Reforming Process 

produces a purge gas containing CH4 that is burned for energy recovery within the methanol 

process. 

Other Production Processes

Methanol may also be produced from the partial oxidation of oil, coal, or petrochemical 

feedstocks, or by gasification of coal to synthesis gas, however; these feedstocks and processes 

currently represent only a small amount of worldwide methanol production. 

ETHYLENE 

Worldwide almost all ethylene is made by way of steam cracking of petrochemical feedstocks. Ethylene may be 

produced from steam cracking of petrochemical feedstocks in a petrochemical plant, and may also be produced 

from cracking and other processes operated at petroleum refineries. Steam cracking for ethylene production also 

produces secondary products including propylene and butadiene. A process description for steam cracking 

process for ethylene production is provided in Box 3.9 below. 

Methanol Steam Reforming Reaction

CH4 + 1⁄2 O2 → CO + 2 H2 → CH3OH

Feedstock Oxidation Reaction

CH4 + O2 → CO2 + 2 H2

Reforming/Shift Reaction

2 CH4 + 3 H2O → CO + CO2 + 7 H2

Methanol Production

CO + CO2 + 7 H2 → 2 CH3OH + 2 H2 + H2O

Steam Reforming

CH4 + H2O → CO + 3 H2

CnHm + nH2O → nCO + (m/2 + n) H2

Shift Reaction

CO + H2O → CO2 + H2

Methanol Production

CO + 2 H2 → CH3OH 

CO2 + 3 H2 → CH3OH + H2O 
Chapter 3: Chemical Industry Emissions 

2006 IPCC Guidelines for National Greenhouse Gas Inventories 3.59 

BOX 3.9 

ETHYLENE PROCESS DESCRIPTION

Steam Cracking

The fundamental chemical equation for ethylene production is as follows: 

The types and mix of feedstock used in steam cracking for ethylene production varies by region, 

and include ethane, propane, butane, naphtha, gas oil, and other petrochemical feedstocks. In the 

United States, most ethylene is produced from steam cracking of ethane, while in Europe, Korea, 

and Japan most ethylene is produced from steam cracking of naphtha. 

Steam cracking of petrochemical feedstocks to produce ethylene also produces other high value 

(saleable) petrochemical products, including propylene, butadiene, and aromatic compounds. Most 

propylene worldwide is produced as a by-product of ethylene production, recovered either from 

steam crackers or from fluid catalytic cracking units at petroleum refineries. Steam crackers using 

naphtha feedstock are the largest source of propylene. There are other process technologies that are 

used to produce propylene including catalytic dehydrogenation of propane. Note that the emissions 

estimation methods in this section apply only to production of ethylene and propylene in steam 

crackers and do not apply to other process technologies used to produce ethylene or propylene. 

The steam cracking process also produces by-product hydrogen and methane and C4+ 

hydrocarbons that are generally burned for energy recovery within the process. 

(Houdek, 2005: Figure 1 on Page 3, Page 4) 

ETHYLENE DICHLORIDE AND VINYL CHLORIDE MONOMER 

Worldwide almost all ethylene dichloride (1, 2 dichloroethane) is made by way of direct chlorination or 

oxychlorination of ethylene, or by a combination of the two processes (referred to as the ‘balanced process.’) An 

example of a feedstock to product process flow diagram for ethylene dichloride production is provided in an 

Annex to Section 3.9 (Annex 3.9A). Process descriptions for ethylene dichloride and vinyl chloride monomer 

production are provided in Box 3.10 below. Note that the chemical compound ‘ethylene dichloride’ is also 

referred to as 1,2-dichloroethane. The chemical compound ‘dichloroethylene,’ also referred to as 1, 2-

dichloroethene, is a different compound. 

BOX 3.10 

ETHYLENE DICHLORIDE AND VINYL CHLORIDE MONOMER PROCESS DESCRIPTIONS

Direct Chlorination and Oxychlorination Processes

The direct chlorination process involves gas-phase reaction of ethylene with chlorine to produce 

ethylene dichloride. The oxychlorination process involves gas-phase reaction of ethylene with 

hydrochloric acid and oxygen to produce ethylene dichloride and water. The ethylene dichloride is 

then cracked to produce vinyl chloride monomer and hydrochloric acid. The oxychlorination 

process produces a process off gas containing by-product CO2 produced from the direct oxidation 

of the ethylene feedstock. 

The fundamental chemical equations for the direct chlorination and oxychlorination processes are 

as follows: 

Direct chlorination 

C2H4 + Cl2 → C2H4Cl2

Oxychlorination reaction

C2H4 + 1⁄2 O2 + 2 HCl 

→ C2H4Cl2 + H2O 

[C2H4 + 3 O2 → 2 CO2 + 2 H2O] 

 Ethylene dichloride>vinyl chloride 

2 C2H4Cl2 → 2 CH2CHCl + 2 HCl 

Ethane Dehydrogenation to Ethylene

C2H6 → C2H4 + H2
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3. 60 2006 IPCC Guidelines for National Greenhouse Gas Inventories 

BOX 3.10 (CONTINUATION) 

ETHYLENE DICHLORIDE AND VINYL CHLORIDE MONOMER PROCESS DESCRIPTIONS

Balanced Process

The combination of the direct chlorination process to produce ethylene dichloride and the ethylene 

dichloride cracking process to produce vinyl chloride monomer produces a surplus of hydrogen 

chloride. The oxychlorination process provides a sink for the hydrogen chloride. Therefore, 

ethylene dichloride/vinyl chloride monomer production facilities may operate a ‘balanced process’ 

in which both the direct chlorination process and the oxychlorination process are combined. The 

‘balanced process’ also produces process vent gas containing by-product CO2 from the direct 

oxidation of the ethylene feedstock. 

The fundamental chemical equations for the ‘balanced process’ for producing vinyl chloride 

monomer from ethylene are as follows: 

The direct chlorination process and the oxychlorination process for ethylene dichloride production 

are not 100 percent efficient in the utilisation of the ethylene feedstock. On the order of three 

percent of the ethylene feedstock is not converted to ethylene dichloride but is converted either to 

CO2 (by direct oxidation in the oxychlorination process) or to other chlorinated hydrocarbons (in 

either the oxychlorination process or the direct chlorination process.) Process off gas containing 

other chlorinated hydrocarbons is generally treated prior to discharge to the atmosphere. The 

chlorinated hydrocarbons are converted to CO2 in a thermal incineration process or a catalytic 

incineration process. Most ethylene dichloride/vinyl chloride monomer plants recover energy from 

the incinerator off gases and process off gases. 

ETHYLENE OXIDE 

Ethylene oxide (C2H4O) is manufactured by reacting ethylene with oxygen over a catalyst. The by-product CO2

from the direct oxidation of the ethylene feedstock is removed from the process vent stream using a recycled 

carbonate solution, and the recovered CO2 may be vented to the atmosphere or recovered for further utilisation 

(e.g., food production.) The oxygen may be supplied to the process through either air or through pure oxygen 

separated from air. An example of a feedstock to product process flow diagram for ethylene oxide production is 

provided in an Annex to Section 3.9 (Annex 3.9A). A process description for ethylene oxide production is 

provided in Box 3.11 below. 

BOX 3.11 

ETHYLENE OXIDE PROCESS DESCRIPTION

The fundamental chemical equations for the production of ethylene oxide from ethylene and the 

production of monoethylene glycol are as follows: 

The ratio of the ethylene oxide reaction and the by-product reaction defines the selectivity of the 

ethylene oxide process, in terms of tonnes of ethylene consumed per tonne of ethylene oxide 

produced. The combined ethylene oxide reaction and by-product CO2 reaction is exothermic and 

generates heat, which is recovered to produce steam for the process. The ethylene oxide process 

also produces other liquid and off-gas by-products (e.g., ethane) that may be burned for energy 

recovery within the process. The amount of CO2 and other by-products produced from the process 

and the amount of steam produced from the process is dependent upon the selectivity of the 

process. 

Ethylene oxide is used as a feedstock in the manufacture of glycols, glycol ethers, alcohols, and 

amines. Worldwide approximately 70 percent of ethylene oxide produced is used in the 

manufacture of glycols, including monoethylene glycol. 

Ethylene Oxide Reaction

C2H4 + 1⁄2 O2 → C2H4O 

Feedstock Oxidation Reaction 

C2H4 + 3 O2 → 2 CO2 + 2 H2O 

Monoethylene Glycol Production

C2H4O + H2O → HO- C2H4 - OH 

Ethylene Dichloride-Vinyl Chloride Monomer Reaction

2 C2H4 + Cl2 + 1⁄2 O2 → 2 CH2CHCl + H2O

Feedstock Oxidation Reaction

[C2H4 + 3 O2 → 2 CO2 + 2 H2O]
Chapter 3: Chemical Industry Emissions 

2006 IPCC Guidelines for National Greenhouse Gas Inventories 3.61 

ACRYLONTRILE 

Worldwide more than 90 percent of acrylonitrile (vinyl cyanide) is made by way of direct ammoxidation of 

propylene with ammonia (NH3) and oxygen over a catalyst. This process is referred to as the SOHIO process, 

after the Standard Oil Company of Ohio (SOHIO). Acrylonitrile can also be manufactured by ammoxidation of 

propane or directly from reaction of propane with hydrogen peroxide. The propane-peroxide direct process has 

recently been commercialised by British Petroleum (BP) and other manufacturers. (DOE, 2000) However, 

process data were not readily available for production of acrylonitrile from propane feedstocks. Therefore no 

emission estimation methodology is provided for this process. An example of a feedstock to product process 

flow diagram for acrylonitrile production from propylene is provided in an Annex to Section 3.9 (Annex 3.9A). 

Process descriptions for acrylonitrile production are provided in Box 3.12 below. 

BOX 3.12 

ACRYLONITRILE PROCESS DESCRIPTION

SOHIO Process

The SOHIO process involves a fluidized bed reaction of chemical-grade propylene, ammonia, and 

oxygen over a catalyst. The catalyst is a mixture of heavy metal oxides (including bismuth and 

molybdenum). The process produces acrylonitrile as its primary product and acetonitrile (methyl 

cyanide) and hydrogen cyanide (HCN) as secondary products. The process yield of the primary 

product acrylonitrile depends in part on the type of catalyst used and the process configuration. 

The ammoxidation process also produces by-product CO2, CO, and water from the direct oxidation 

of the propylene feedstock, and produces other hydrocarbons from side reactions in the 

ammoxidation process. 

The acetonitrile and hydrogen cyanide are separated from the acrylonitrile by absorption, and the 

hydrogen cyanide may be used in manufacturing other products on site or sold as product. 

Hydrogen cyanide that is not used or sold may be burned for energy recovery or flared. The 

acetonitrile may be also recovered for sale as a product, but more often the acetonitrile is burned 

for energy recovery or flared. The off gas from the main absorber vent containing CO2, CO, 

nitrogen, water, unreacted propylene, and other hydrocarbons, may be flared or treated in a thermal 

or catalytic oxidation unit, with or without energy recovery. 

Heavy bottoms liquids from the acetonitrile – hydrogen cyanide - acrylonitrile absorption 

separations process may also be burned for energy recovery or recycled. Acrylonitrile and other 

non-methane hydrocarbons are also released from miscellaneous process vents, including storage 

tanks. These miscellaneous process vents may be flared or captured and burned for energy 

recovery. 

The fundamental chemical equations for the production of acrylonitrile by ammoxidation are as 

follows: 

The ammoxidation of propylene to acrylonitrile is not 100 percent efficient in utilisation of the 

propylene feedstock. On the order of 70 percent of the propylene feedstock is converted to 

acrylonitrile. On the order of 85 percent of the propylene feedstock is converted to either the 

primary product acrylonitrile or secondary products acetonitrile or hydrogen cyanide. The 

remainder of the propylene feedstock is either converted directly to CO2 by direct oxidation of the 

feedstock in the ammoxidation process or converted to other hydrocarbons through side reactions 

in the ammoxidation process. 

CARBON BLACK 

Worldwide almost all carbon black is produced from petroleum-based or coal-based feedstocks using the 

‘furnace black’ process. Process descriptions for carbon black production are provided in Box 3.13 below. 

Acrylonitrile Reaction

CH2=CHCH3 + 1.5 O2 + NH3 

→ CH2=CHCN + 3 H2O 

Hydrogen Cyanide Reaction 

CH2=CHCH3 + 3 O2 + 3 NH3 → 3 HCN + 6 H2O 

Acetonitrile Reaction

CH2=CHCH3 + 1.5 O2 + 1.5 NH3 

→ 1.5 CH3CN + 3 H2O 

Feedstock Oxidation

C3H6 + 4.5 O2 → 3 CO2 + 3 H2O 

C3H6 + 3 O2 → 3 CO + 3 H2O 
Volume 3: Industrial Processes and Product Use 

3. 62 2006 IPCC Guidelines for National Greenhouse Gas Inventories 

The furnace black process is a partial combustion process where a portion of the carbon black feedstock is 

combusted to provide energy to the process. Carbon black may also be produced using other petroleumfeedstock or coal-based feedstock partial oxidation processes, including the ‘channel black’ process and ‘lamp 

black’ process, or may be produced directly by the partial oxidation of natural gas or aromatic oils (‘channel 

black process’). Carbon black may also be produced by the thermal cracking of acetylene-containing feedstocks 

(‘acetylene black process’) or by the thermal cracking of other hydrocarbons (‘thermal black process’.) 

Approximately 95 percent of worldwide carbon black production is by way of the furnace black process; the 

remaining 5 percent being produced by way of other processes. 

Approximately 90 percent of carbon black produced worldwide is used in the tire and rubber industry (referred 

to as ‘rubber black.’) and the remainder is used in pigment applications (e.g., inks) and other applications (e.g., 

carbon dry cell batteries.) Carbon black may be produced using a furnace black process, thermal black process, 

acetylene carbon black process, channel black process and lamp black process. These processes are further 

described in Box 3.13 below. An example of a feedstock to product process flow diagram for carbon black 

production using the furnace black process is provided in an Annex to Section 3.9 (Annex 3.9A). 

BOX 3.13 

CARBON BLACK PRODUCTION PROCESS DESCRIPTIONS

Furnace Black Process

The furnace black process produces carbon black from ‘carbon black feedstock’ (also referred to 

as ‘carbon black oil’) which is a heavy aromatic oil that may be derived either as a by-product of 

the petroleum refining process or the metallurgical (coal) coke production process. For either 

petroleum-derived or coal-derived feedstock, the carbon black feedstock, the ‘primary feedstock,’ 

is injected into a furnace heated by a ‘secondary feedstock’ (generally natural gas or oil). Both the 

natural gas secondary feedstock and a portion of the carbon black feedstock are oxidized to 

provide heat to the production process that pyrolyzes the remaining carbon black feedstock to 

carbon black. The vent gas from the furnace black process contains CO2, CO, sulphur compounds, 

CH4, and NMVOCs. A portion of the tail gas is generally burned for energy recovery to heat the 

downstream carbon black product dryers. The remaining tail gas may also be burned for energy 

recovery, flared, or vented uncontrolled to the atmosphere. 

Thermal Black Process

Carbon black is produced in the thermal black process by thermal decomposition of gaseous 

hydrocarbons or atomized petroleum oils in the absence of air in a pair of production furnaces. 

The carbon black feedstock is introduced into a preheated furnace that is heated by a secondary 

feedstock, usually natural gas, and by the off gas from the carbon black production process. One of 

the pair of furnaces is being preheated by the secondary feedstock while the other furnace is 

receiving carbon black feedstock. Yield from this process is approximately 45 percent of total 

carbon input to the process (or 40 percent with respect to the total carbon black feedstock used) 

and energy utilisation is approximately 280 MJ/kg carbon black produced. 

Acetylene Black Process 

Carbon black produced from acetylene or acetylene-containing light hydrocarbons by feeding the 

feedstock to a preheated reactor where the acetylene decomposes to carbon black in an exothermic 

process. Total worldwide production of acetylene black is only approximately 40 000 metric tons 

per year. The carbon black yield from this process is approximately 95-99 percent of theoretical 

yield. Acetylene black is approximately 99.7 percent carbon. 

Other Production Processes 

The channel black process involves partial oxidation of vaporised carbon black feedstock that is 

burned in a furnace with a carrier gas (which may be coke oven gas, hydrogen, or methane). The 

carbon black yield for this process may be 60 percent of total carbon input for production of 

rubber-grade carbon black or 10-30 percent of total carbon input for pigment-grade carbon black. 

The lamp black process involves open burning of carbon black feedstock in shallow pans. Data are 

not readily available concerning feedstock yield and energy consumption for the lamp black 

process. This process represents an insignificant percentage of worldwide carbon black production. 

(Kirk Othmer, 1992) 
Chapter 3: Chemical Industry Emissions 

2006 IPCC Guidelines for National Greenhouse Gas Inventories 3.63 

3.9.2 Methodological issues 

3.9.2.1 CHOICE OF METHOD

The emissions from petrochemical and carbon black production vary both with the process used and the 

feedstock used. The choice of method should thus be repeated for each product, process and feedstock used. 

Three methodological tiers are provided depending on the availability of data. The choice of method depends on 

national circumstances and is given by the decision trees in Figure 3.8 and Figure 3.9. 

Figure 3.8 Decision tree for estimation of CO2 emissions from petrochemical industry 

and carbon black industry 

Start

Are

both the type

of feedstock used and 

process

known?

Is

Petrochemical

and Carbon Black

Production a key category and 

is this subcategory

significant?

Is it the

process that is

unknown?

No

No

No

Collect 

feedstock

and the

process 

data1

.

Estimate emissions 

using Tier 3

plant-specific 

emission factors.

Estimate emissions using Tier 1 default 

emission factors using Equation 3.15.

Box 1: Tier 1

Box 4: Tier 3

Note:

1. See Volume 1 Chapter 4,"Methodological Choice and Identification of Key Categories" (noting Section 4.1.2 on limited resources), for 

discussion of key categories and use of decision trees.

Yes

No

Is it the

feedstock that is

 unknown?

Estimate emissions

using Tier 2 carbon

balance.

Estimate emissions using Tier 1 default 

emission factors using Equation 3.15. If 

the annual primary product production 

data are not available, use Equation 3.16.

Box 3: Tier 2

Box 2: Tier 1

Yes

Yes

Is

supplementary

fossil fuel transferred 

into the process?

Are

by-products

transferred out of the 

process?

Are the

activity data for

all carbon flows

available?

Are

plant-specific

emission factors 

available?

Assume default

process.

Subtract

carbon

from carbon

balance.

Add carbon emitted to

carbon balance.

Assume default feedstock.

Repeat for each

feedstock and 

petrochemical.

Yes

No

No

Yes

No

Yes

Yes

No

Yes
Volume 3: Industrial Processes and Product Use 

3. 64 2006 IPCC Guidelines for National Greenhouse Gas Inventories 

Figure 3.9 Decision tree for estimation of CH4 emissions from petrochemical industry 

and carbon black industry 

Start

Are

both the type

of feedstock used and 

process

known?

Is

Petrochemical

and Carbon Black

Production a key category and 

is this subcategory

significant?

Is it the

process that is

unknown?

No

No

No

Collect 

feedstock

and the

process 

data1

.

Estimate emissions 

using Tier 3

plant-specific 

emission factors.

Estimate emissions using Tier 1 default 

emission factors.

Box 1: Tier 1

Box 3: Tier 3

Note:

1. See Volume 1 Chapter 4,"Methodological Choice and Identification of Key Categories" (noting Section 4.1.2 on limited resources), for 

discussion of key categories and use of decision trees.

2. Note that there is no Tier 2 method for estimating CH4 emissions. The Tier 2 method is a total feedstock carbon mass balance method 

that is applicable to estimating total carbon (CO2) emissions but not applicable to estimating CH4 emissions.

Yes

No

Is it the

feedstock that is

 unknown?

Estimate emissions using Tier 1 default 

emission factors. If the annual primary 

product production data are not 

available, use Equation 3.16.

Box 2: Tier 1

Yes

Yes

Are

plant-specific

emission factors 

available?

Assume default

process.

Assume default feedstock.

Repeat for each

feedstock and 

petrochemical.

Yes

No

Yes

The Tier 3 methodology can be used to estimate plant-level CO2 emissions and CH4 emissions. The Tier 3 

method depends upon the availability of plant-specific data for the petrochemical process. The Tier 2 

methodology is a mass balance approach that is applicable to estimating CO2 emissions but is not applicable to 

estimating CH4 emissions. When using the Tier 2 methodology, both carbon flows of primary and secondary 

feedstocks to the process are included in the mass balance calculation. Carbon flows of primary fuels to the 
Chapter 3: Chemical Industry Emissions 

2006 IPCC Guidelines for National Greenhouse Gas Inventories 3.65 

process may involve combustion of part of the hydrocarbon content for heat raising and the production of 

secondary fuels (e.g., off gases). In order to apply the Tier 2 methodology the flows of primary and secondary 

feedstocks to the process and the flows of primary and secondary products must be characterised, and the flows 

of by-products burned for energy recovery within the process and flows of by-products transferred out of the 

process must be characterised. 

CARBON DIOXIDE 

The decision tree for choice of method for CO2 emissions is shown in Figure 3.8. The Tier 1, Tier 2, and Tier 3 

methods are described in this section. 

Tier 1 product-based emission factor method 

The Tier 1 emission factor methodology is applied to estimate CO2 emissions from the petrochemical process in 

cases where neither plant specific data nor activity data for carbon flows are available for the petrochemical 

process. The Tier 1 emission factor method does not require activity data for the consumption of each carboncontaining feedstock to the petrochemical production process. It requires only activity data for the amount of 

product produced. The Tier 1 methodology does not consider the carbon content of emissions of carbon 

monoxide or NMVOC that may be generated by the petrochemical processes. The equations in this section for 

petrochemical production processes also apply to carbon black production. 

The Tier 1 method calculates emissions from petrochemical processes on the basis of activity data for production 

of each petrochemical and the process-specific emission factor for each petrochemical, as shown in the Equation 

3.15 for production of each primary petrochemical product (e.g., methanol, ethylene, ethylene dichloride, 

ethylene oxide, acrylonitrile) and carbon black. 

EQUATION 3.15 

TIER 1 CO2 EMISSION CALCULATION

ECO2i = PPi • EFi •GAF /100

Where: 

ECO2i = CO2 emissions from production of petrochemical i, tonnes 

PPi = annual production of petrochemical i, tonnes 

EFi = CO2 emission factor for petrochemical i, tonnes CO2/tonne product produced 

GAF = Geographic Adjustment Factor (for Tier 1 CO2 emission factors for ethylene production, See 

Table 3.15), percent 

Tier 1 CO2 emission factors for ethylene production (discussed in Section 3.9.2.2) have been developed based on 

data for ethylene steam crackers operating in Western Europe. Geographic Adjustment Factors are applied to the 

Tier 1 emission factor to account for regional variability in steam cracker operating efficiency. Geographic 

Adjustment Factors are only applicable to ethylene production. 

If activity data for annual primary product production are not available, primary product production may be 

estimated from feedstock consumption, as shown in the Equation 3.16: 

EQUATION 3.16 

PRIMARY PRODUCT PRODUCTION ESTIMATE CALCULATION

= ∑( • )

k

i i k i k PP FA, SPP,

Where: 

PPi = annual production of petrochemical i, tonnes 

FAi,k = annual consumption of feedstock k consumed for production of petrochemical (i), tonnes 

SPPi,k = specific primary product production factor for petrochemical i and feedstock k ,tonnes primary 

product/tonne feedstock consumed 

Either Equation 3.15 or both Equation 3.15 and Equation 3.16 would be applied separately to each of the known 

feedstocks for each petrochemical process. The Tier 1 emissions estimate shown in Box 1 of Figure 3.8 would 

utilise Equation 3.15, while the Tier 1 emissions estimate shown in Box 2 of Figure 3.8 would use either 
Volume 3: Industrial Processes and Product Use 

3. 66 2006 IPCC Guidelines for National Greenhouse Gas Inventories 

Equation 3.15 or both Equation 3.16 and Equation 3.15. Equation 3.15 would be utilised alone in cases where 

annual primary product production data are available for the petrochemical process. In cases where annual 

primary product production data are not available but feedstock consumption data are available for the 

petrochemical process, Equation 3.16 would be utilised to estimate the annual production of primary products, 

and the annual primary product production estimated using Equation 3.16 would then be applied in Equation 

3.15 to estimate the emissions. 

Tier 2 total feedstock carbon balance method 

The Tier 2 method is a feedstock-specific and process-specific carbon balance approach. This approach is 

applicable in cases where activity data are available for both feedstock consumption and primary and secondary 

product production and disposition. Activity data for all carbon flows are required to implement the Tier 2 

methodology. Examples of process flow diagrams that illustrate feedstock and product flows for the methanol, 

ethylene dichloride, ethylene oxide, acrylonitrile, and carbon black production processes are included in an 

Annex to Section 3.9. The number of potential feedstocks and products for ethylene production from the steam 

cracking process is such that the process is better illustrated by a feedstock-product matrix rather than by a 

process flow diagram. The feedstock-product matrix for ethylene production is included in Table 3.25 in Section 

3.9.2.3. A flow diagram of the Tier 2 method is shown in Figure 3.10.

Figure 3.10 Tier 2 carbon mass balance flow diagram 

Identify Primary

Feedstock to

Process.

Determine Primary

Product Carbon

Content using Table

3.10 or activity data.

Calculate carbon emissions from process using Equation 3.17.

Identify Petrochemical Production Process.

Calculate carbon output

{[PPi・PCi + ∑j(SPi,j・SCj)] in

Equation 3.17}

Calculate carbon input

{∑k(FAi,k・FCk) in Equation 3.17}

Determine Secondary 

Product Carbon Content

using Table 3.10 or

activity data.

Determine Secondary

Feedstock Carbon

Content using Table

3.10 or activity data.

Determine Primary

Feedstock Carbon

Content using Table

3.10 or activity data.

Determine Secondary 

Product Production

using activity data or

Table 3.25 and

Equation 3.18

(ethylene) or Table

3.26 and Equation

3.19 (acrylonitrile).

Determine Primary

Product Production

using activity data.

Determine Secondary

Feedstock

Consumption using

activity data.

Determine Primary

Feedstock

Consumption using

activity data.

Identify Secondary

Product(s) of

Process.

Identify Primary

Product of

Process.

Identify Secondary

Feedstock(s) to

Process.
Chapter 3: Chemical Industry Emissions 

2006 IPCC Guidelines for National Greenhouse Gas Inventories 3.67 

The Tier 2 method calculates the difference between the total amount of carbon entering into the production 

process as primary and secondary feedstock and the amount of carbon leaving the production process as 

petrochemical products. The difference in carbon content of the primary and secondary feedstocks and the 

carbon content of the primary and secondary products produced by and recovered from the process is calculated 

as CO2. The Tier 2 mass balance methodology is based on the assumption that all of the carbon input to the 

process is converted either into primary and secondary products or into CO2. This means that any of the carbon 

input to the process that is converted into CO, CH4, or NMVOC are assumed to be CO2 emissions for the 

purposes of the mass balance calculation. 

The overall mass balance equation for the Tier 2 methodology is Equation 3.17. 

EQUATION 3.17 

OVERALL TIER 2 MASS BALANCE EQUATION 

2 ( ) , ( ) , • 44 12 ⎪⎭

⎪

⎬

⎫

⎪⎩

⎪

⎨

⎧

⎥

⎥

⎦

⎤

⎢

⎢

⎣

⎡ = ∑ • − • + ∑ • j

i i i j j

k

ECO i FAi k FCk PP PC SP SC

Where: 

ECO2i = CO2 emissions from production of petrochemical i, tonnes 

FAi,k = annual consumption of feedstock k for production of petrochemical i, tonnes 

FCk = carbon content of feedstock k, tonnes C/tonne feedstock 

PPi = annual production of primary petrochemical product i, tonnes 

PCi = carbon content of primary petrochemical product i, tonnes C/tonne product 

SPi,j = annual amount of secondary product j produced from production process for petrochemical i, 

tonnes 

[The value of SPi,j is zero for the methanol, ethylene dichloride, ethylene oxide, and carbon black 

processes because there are no secondary products produced from these processes. For ethylene 

production and acrylonitrile production, see secondary product production Equations 3.18 and 3.19 

below to calculate values for SPi,j.] 

SCj = carbon content of secondary product j, tonnes C/tonne product 

For ethylene production and acrylonitrile production there are both primary and secondary products produced by 

the process. If activity data are not available for the amount of secondary products produced by these processes, 

the amount of secondary products produced may be estimated by applying default values to the primary 

feedstock consumption, as shown in Equations 3.18 and 3.19: 

EQUATION 3.18 

ESTIMATE SECONDARY PRODUCT PRODUCTION FROM PRIMARY PRODUCT [ETHYLENE]

PRODUCTION

= ∑( • )

k

Ethylene j Ethylene k j k SP , FA , SSP ,

Where: 

SPEthylene ,j = annual production of secondary product j from ethylene production, tonnes 

FAEthylene k = annual consumption of feedstock k consumed for ethylene production, tonnes 

SSPj,k = specific secondary product production factor for secondary product j and feedstock k, tonnes 

secondary product/tonne feedstock consumed 

EQUATION 3.19 

ESTIMATE SECONDARY PRODUCT PRODUCTION FROM PRIMARY PRODUCT [ACRYLONITRILE]

PRODUCTION

= ∑( • )

k

Acrylonitrile j Acrylonitrile k j k SP , FP , SSP ,

Where: 
Volume 3: Industrial Processes and Product Use 

3. 68 2006 IPCC Guidelines for National Greenhouse Gas Inventories 

SP Acrylonitrile,j = annual production of secondary product j from acrylonitrile production, tonnes 

FP Acrylonitrile,k = annual production of acrylonitrile from feedstock k, tonnes 

SSPj,k = specific secondary product production factor for secondary product j and feedstock k, tonnes 

secondary product/tonne acrylonitrile produced 

Note: It is anticipated that in most cases only a single feedstock (propylene) would be used for 

acrylonitrile production. 

Feedstock and product carbon contents 

Carbon contents of feedstocks and products of petrochemical production processes are listed in Table 3.10, in 

units of tonnes of carbon per tonne of feedstock or product. Carbon contents of pure substances (e.g., methanol) 

are calculated from the chemical formula. Carbon contents of other feedstocks and products (e.g., carbon black 

feedstock, carbon black) are estimated from literature sources. Representative carbon contents of fossil fuels 

(e.g., natural gas, naphtha) can be found in Table 1.3 in Chapter 1 of Volume 2: Energy; however, carbon 

contents for fossil fuels will vary by country and region and are best obtained from national energy statistics or 

fossil fuel product specifications or national standards. 

Tier 3 direct estimate of plant-specific emissions 

The most rigorous good practice method is to use plant specific data to calculate CO2 emissions from the 

petrochemical production process. In order to apply the Tier 3 method, plant-specific data and/or plant-specific 

measurements are required. The emissions from the petrochemical production process include CO2 emitted from 

fuel or process by-products combusted to provide heat or thermal energy to the production process, CO2 emitted 

from process vents, and CO2 emitted from flared waste gases. These emissions are calculated using Equations 

3.20 through 3.22. 

Overall CO2 emissions from the petrochemical production process are calculated using Equation 3.20 

EQUATION 3.20 

TIER 3 CO2 EMISSIONS CALCULATION EQUATION

ECO2i = ECombustion,i + EProcess Vent,i + EFlare,i

Where: 

ECO2i = CO2 emissions from production of petrochemical i, tonnes 

E Combustion,i = CO2 emitted from fuel or process by-products combusted to provide heat or thermal energy 

to the production process for petrochemical i, tonnes 

E Process Vent,i = CO2 emitted from process vents during production of petrochemical i, tonnes 

E Flare,i = CO2 emitted from flared waste gases during production of petrochemical i, tonnes 

E combustion and E flare are given by Equations 3.21 and 3.22 where plant specific or national net calorific value data 

should be used. The emission factor is given by the carbon content of the fuel, the combustion oxidation factor 

and a constant (44/12) converting the result from carbon to CO2. If the emission factor is not known a default 

value may be found in Table 1.4 in Chapter 1 of Volume 2: Energy. Net calorific values are included in Table 

1.2 in Chapter 1 of Volume 2: Energy. Carbon contents are included in Table 1.3 in Chapter 1 of Volume 2: 

Energy. For the process vents, inventory compilers should measure/estimate emissions of CO2 directly and thus 

no further equation is provided. 

EQUATION 3.21 

FUEL COMBUSTION TIER 3 CO2 EMISSIONS CALCULATION

= ∑( • • )

k

ECombustion,i FAi,k NCVk EFk

Where: 

FAi,k = amount of fuel k consumed for production of petrochemical i, tonnes 

NCVk = net calorific value of fuel k, TJ/tonne 

(Note: In Table 1.2 in Chapter 1 of Volume 2, net calorific values are expressed in TJ/kg) 
Chapter 3: Chemical Industry Emissions 

2006 IPCC Guidelines for National Greenhouse Gas Inventories 3.69 

EFk = CO2 emission factor of fuel k, tonnes CO2/TJ 

(Note: In Table 1.4 in Chapter 1 of Volume 2, CO2 emission factors are expressed in kg/TJ) 

EQUATION 3.22 

FLARE GAS TIER 3 CO2 EMISSIONS CALCULATION

= ∑( • • )

k

EFlare,i FGi,k NCVk EFk

Where: 

FGi,k = amount of gas k flared during production of petrochemical i, tonnes 

NCVk = net calorific value of flared gas k, TJ/tonne 

(Note: In Table 1.2 in Chapter 1 of Volume 2, net calorific values are expressed in TJ/kg) 

EFk = CO2 emission factor of flared gas k, tonnes CO2/TJ 

(Note: In Table 1.4 in Chapter 1 of Volume 2, CO2 emission factors are expressed in kg/TJ) 

TABLE 3.10 

SPECIFIC CARBON CONTENT OF PETROCHEMICAL FEEDSTOCKS AND PRODUCTS

Substance Carbon (tonne carbon per tonne feedstock or 

product) 

Acetonitrile 0.5852 

Acrylonitrile 0.6664 

Butadiene 0.888 

Carbon black 0.970 

Carbon Black Feedstock 0.900 

Ethane 0.856 

Ethylene 0.856 

Ethylene dichloride 0.245 

Ethylene glycol 0.387 

Ethylene oxide 0.545 

Hydrogen Cyanide 0.4444 

Methanol 0.375 

Methane 0.749 

Propane 0.817 

Propylene 0.8563 

Vinyl Chloride Monomer 0.384 

Note: Carbon content values for natural gas and naphtha vary by country and region. Net 

calorific values (NCV) for natural gas, naphtha, and other primary fuels that may be used as 

petrochemical feedstocks are included in Table 1.2 in Chapter 1 of Volume 2: Energy. 

Feedstock carbon contents are included in Table 1.3 in Chapter 1 of Volume 2: Energy. 

METHANE 

The decision tree for choice of method for CH4 emissions is shown in Figure 3.9. The Tier 1 and Tier 3 methods 

for CH4 are described in this section. There is no Tier 2 method applicable to CH4 emissions. 

Tier 1 product-based emission factor method 

CH4 emissions from petrochemical processes may be fugitive emissions and/or process vent emissions. Fugitive 

emissions are emitted from flanges, valves, and other process equipment. Emissions from process vent sources 

include incomplete combustion of waste gas in flare and energy recovery systems. CH4 emissions using the Tier 

1 method may be calculated using Equation 3.23 for fugitive CH4 emissions and Equation 3.24 for process vent 
Volume 3: Industrial Processes and Product Use 

3. 70 2006 IPCC Guidelines for National Greenhouse Gas Inventories 

emissions and Equation 3.25 for total CH4 emissions. If annual primary product production data are not available 

but feedstock consumption data are available for the petrochemical process, Equation 3.16 would be utilised to 

estimate the annual production of primary products, and the annual primary product production estimated using 

Equation 3.16 would then be applied in Equations 3.23 and 3.24 to estimate the emissions. 

EQUATION 3.23 

TIER 1 CH4 FUGITIVE EMISSION CALCULATION

ECH Fugitive i PPi EFfi = • 4 ,

EQUATION 3.24 

TIER 1 CH4 PROCESS VENT EMISSION CALCULATION

ECH ProcessVent i PPi EFpi = • 4 ,

EQUATION 3.25 

TIER 1 CH4 TOTAL EMISSIONS CALCULATION

ECH 4Total,i = ECH 4Fugitive,i + ECH 4ProcessVent,i

Where: 

ECH4 Total,i = total emissions of CH4 from production of petrochemical i, kg 

ECH4 Fugitive,i = fugitive emissions of CH4 from production of petrochemical i, kg 

ECH4 Process Vent,i = process vent emissions of CH4 from production of petrochemical i, kg 

PPi = annual production of petrochemical i, tonnes 

EFfi = CH4 fugitive emission factor for petrochemical i, kg CH4/tonne product 

EFpi = CH4 process vent emission factor for petrochemical i, kg CH4/tonne product 

Tier 2 total feedstock carbon balance method 

The total feedstock carbon mass balance method is not applicable to estimation of CH4 emissions. The total 

carbon mass balance method estimates the total carbon emissions from the process but does not directly provide 

an estimate of the amount of the total carbon emissions that is emitted as CO2, CH4, CO, or NMVOC. 

Tier 3 direct estimate of plant-specific emissions 

The Tier 3 method is based on continuous or periodic plant-specific measurements. The emissions from the 

petrochemical production process include CH4 emitted from fuel or process by-products combusted to provide 

heat or thermal energy to the production process, CH4 emitted from process vents, and CH4 emitted from flared 

waste gases. If methane is vented directly to the atmosphere this will dominate the emissions. CH4 emissions 

from process vents may also be combusted in a flare or energy recovery device. Measurement of atmospheric 

concentration of VOCs directly above the plants or in the plume is the preferred activity data for estimating 

fugitive CH4 emissions; however, such data may not be available. The atmospheric measurements are generally 

expensive and will most often not be continuous measurements but rather a discrete and periodic measurement 

program to obtain data to be used as basis for the development of plant specific emission factors. The results of 

such measurement programs would then be related to other plant process parameters to enable estimation of 

emissions between measurement periods. 

Direct measurement of VOC and CH4 concentrations in plant exhaust gas streams and direct measurement of 

fugitive VOC and CH4 emissions from plant valves, fittings, and related equipment using a comprehensive leak 

detection programme can also be used to obtain plant-specific activity data for developing Tier 3 estimates of 

CH4 emissions. However the plant-specific leak detection programme should provide fugitive CH4 emissions 

data for all of the relevant CH4-emitting plant equipment. Similarly, the plant-specific measurement data for 

stacks and vents would need to cover the major portion of stack and vent CH4 emissions sources at the plant in 

order to provide a basis for a Tier 3 emission calculation. 
Chapter 3: Chemical Industry Emissions 

2006 IPCC Guidelines for National Greenhouse Gas Inventories 3.71 

Emissions of CH4 from process stacks and vents may be estimated by direct measurement of the CH4

concentration of the exhaust gas or estimated as a component of the total VOC concentration measured in the 

exhaust gas. Fugitive emissions of CH4 from plant equipment (e.g., valves, fittings) may be estimated through 

application of plant-specific leak detection data and plant equipment inventories, provided that the plant-specific 

leak detection program and equipment inventory are comprehensive, such that the program provides fugitive 

CH4 emissions data for all of the relevant CH4-emitting plant equipment. Similarly, the plant-specific 

measurement data for stacks and vents would need to cover the major portion of stack and vent CH4 emissions 

sources at the plant in order to provide a basis for a Tier 3 emission calculation. 

Measurement of fugitive emissions may also be based on the CH4 concentration in the atmosphere immediately 

above the plant or in a plume downwind. Such atmospheric measurement data would generally measure 

emissions from the entire plant, and does not separate between the different sources. In addition to CH4

concentration the area of the plume and the wind speed must be measured. The emissions are given by Equation 

3.26. 

EQUATION 3.26 

TIER 3 CH4 EMISSION CALCULATION BASED ON ATMOSPHERIC MEASUREMENT DATA

[ ] ( ) ∫ = • − • • CH 4 Emissions t Ctotal VOCs CH 4 fraction CH 4background level WS PA

Where: 

CH4 Emissions = total plant CH4 emissions, μg/s 

C total VOCs = VOC concentration at the plant, μg/m3

CH4 fraction = fraction of total VOC concentration that is CH4, fraction 

CH4 background level = ambient CH4 concentration at background location, μg/m3 

WS = wind speed at the plant, m/s 

PA = plume area, m2 

Note: ∫t means the quantity should be summed over time. 

Note that the Tier 3 methodology does not direct inventory compilers to conduct atmospheric measurements or 

other specific types of direct measurements to estimate site-specific CH4 emissions. It is anticipated that plantspecific leak detection data and plant-specific stack and vent emission data will be more readily available than 

atmospheric measurement data. However, if atmospheric measurement data are available the data may be used 

to develop Tier 3 estimates of CH4 emissions, or to verify other estimates. Atmospheric measurement data may 

provide a more accurate estimate of process CH4 emissions than leak detection data and stack and vent emission 

data. A plant would use either i) Equation 3.26 or ii) Equations 3.27, 3.28, and 3.29 to estimate CH4 emissions.

Process vent emissions are assumed to be monitored either discretely or continuously. The method of calculation 

will vary depending upon the type of data, and therefore no separate equation is provided for process vent 

emissions calculation. 

Overall emissions of CH4 from the petrochemical production process based on plant-specific leak detection data 

and plant-specific stack and vent emissions data are calculated using Equation 3.27 

EQUATION 3.27 

TIER 3 CH4 EMISSIONS CALCULATION EQUATION

ECH 4i = ECombustion,i + EProcess Vent,i + EFlare,i

Where: 

ECH4i = total emissions of CH4 from production of petrochemical i, kg 

E Combustion,i = emissions of CH4 from fuel or process by-products combusted to provide heat or thermal 

energy to the production process for petrochemical i, kg 

E Process Vent,i = emissions of CH4 from process vents during production of petrochemical i, kg 

E Flare,i = emissions of CH4 from flared waste gases during production of petrochemical i, kg 

E combustion and E flare are given by Equations 3.28 and 3.29 where plant specific or national net calorific value data 

should be used. 
Volume 3: Industrial Processes and Product Use 

3. 72 2006 IPCC Guidelines for National Greenhouse Gas Inventories 

EQUATION 3.28 

FUEL COMBUSTION TIER 3 CH4 EMISSIONS CALCULATION

= ∑( • • )

k

ECombustion,i FAi,k NCVk EFk

Where: 

FAi,k = amount of fuel k consumed for production of petrochemical i, tonnes 

NCVk = net calorific value of fuel k, TJ/tonne 

(Note: In Table 1.2 in Chapter 1 of Volume 2, net calorific values are expressed in TJ/kg) 

EFk = CH4 emission factor of fuel k, kg/TJ 

EQUATION 3.29 

FLARE GAS TIER 3 CH4 EMISSIONS CALCULATION

= ∑( • • )

k

EFlare,i FGi,k NCVk EFk

Where: 

FGi,k = amount of gas k flared during production of petrochemical i, tonnes 

NCVk = net calorific value of flared gas k, TJ/tonne 

(Note: In Table 1.2 in Chapter 1 of Volume2, net calorific values are expressed in TJ/kg) 

EFk = CH4 emission factor of flared gas k, kg/TJ 

3.9.2.2 CHOICE OF EMISSION FACTORS

This section includes a discussion of the choice of emission factors for the Tier 1 method. The Tier 2 method is 

based on mass balance principles and the Tier 3 method is based on plant-specific data; therefore there are no 

default emission factors applicable to the Tier 2 and Tier 3 methods. 

TABLE 3.11 

PETROCHEMICAL PRODUCTION TIER 1 DEFAULT FEEDSTOCKS AND PROCESSES

Petrochemical Process Default Feedstock Default Process 

Methanol Natural Gas Conventional steam reforming without primary 

reformer 

Ethylene North America, South America, 

Australia - Ethane 

Other Continents - Naphtha 

Steam cracking 

Steam cracking 

Ethylene Dichloride / 

Vinyl Chloride Monomer 

Ethylene Balanced Process for EDC production with 

integrated VCM production plant 

Ethylene Oxide Ethylene Catalytic Oxidation, Air Process, with thermal 

treatment 

Acrylonitrile Propylene Direct Ammoxidation with secondary products 

burned for energy recovery or flared 

Carbon Black Carbon black feedstock and natural gas Furnace black process with thermal treatment 

TIER 1 

Tier 1 emission factors for CO2 emissions and CH4 emissions for petrochemical products are provided below. 

Tier 1 emission factors for CO2 emissions do not include carbon emitted as CO, CH4, or NMVOC. Separate Tier 

1 emission factors are provided for CH4 emissions from petrochemical processes. Tier 1 emission factors are not 

provided for carbon monoxide and NMVOC emissions. 

The Tier 1 method allows for the selection of a ‘default’ feedstock and ‘default’ process in instances where 

activity data are not available to identify the feedstock or the process utilised to produce the petrochemical. 

Table 3.11 provides the default feedstocks and default processes for each petrochemical production process. In 
Chapter 3: Chemical Industry Emissions 

2006 IPCC Guidelines for National Greenhouse Gas Inventories 3.73 

the event that no activity data are available concerning the specific processes and feedstocks used within a 

country to produce the petrochemical, the default process and default feedstock identified in Table 3.11 and the 

associated Tier 1 emission factors identified in the subsequent tables in this section are used to estimate the CO2

emissions from the petrochemical production process. Country-specific emission factors may be used instead of 

the default emission factors if country-specific factors are available. 

Methanol 

Carbon dioxide emissions 

Emissions of CO2 from methanol production from the steam reforming and partial oxidation processes may be 

estimated by applying the default process feedstock emission factors, or the feedstock-specific and processspecific emission factors in Table 3.12, to activity data for methanol production, process configuration and 

process feedstock. The default emission factors are based on the average of plant-specific CO2 emissions data 

reported for four methanol plants using the conventional steam reforming process without primary reformer and 

using natural gas feedstock. Emissions data used in developing the default CO2 emission factor were reported 

for conventional process methanol plants in New Zealand, Chile, and Canada and in the Netherlands. Emission 

factors in the table include both the CO2 emissions arising from the process feedstock and the CO2 emissions 

arising from feedstock combusted within the steam reforming process. Table 3.13 summarises the total feedstock 

consumption, in units of GJ/tonne methanol produced, for the various methanol production process 

configurations and feedstocks shown in Table 3.12. 

The conventional reforming process can include a single reformer unit or both a primary reformer unit and a 

secondary reformer. The emission factors differ depending upon the number of reformer units. Lurgi is a 

provider of methanol process technology and has published emission factors for several conventional reforming 

process technologies, see Table 3.12. The production capacity of Mega Methanol plants is generally greater than 

5 000 tonnes per day of methanol. The emission factors for the Lurgi Conventional process technologies should 

be applied only if the specific process technology is known. Otherwise the emission factor for conventional 

steam reforming without primary reformer, or the emission factor for conventional steam reforming with primary 

reformer, should be applied. 

The conventional steam reforming process for methanol production can be integrated with an ammonia 

production process. The emission factor for integrated methanol and ammonia production should be used only if 

the specific process technology is known. 

TABLE 3.12 

METHANOL PRODUCTION CO2 EMISSION FACTORS

 tonne CO2/tonne methanol produced 

Process Configuration Feedstock Nat. gas Nat. gas + 

CO2

Oil Coal Lignite

Conventional Steam Reforming, without primary reformer (a) 

(Default Process and Natural Gas Default Feedstock) 0.67 

Conventional Steam Reforming, with primary reformer (b) 0.497 

Conventional Steam Reforming, Lurgi Conventional process (c1) 0.385 0.267 

Conventional Steam Reforming, Lurgi Low Pressure Process (c2) 0.267 

Combined Steam Reforming, Lurgi Combined Process (c3) 0.396 

Conventional Steam Reforming, Lurgi Mega Methanol Process (c4) 0.310 

Partial oxidation process (d) 1.376 5.285 5.020 

Conventional Steam Reforming with integrated ammonia production 1.02 

Nat. gas + CO2 feedstock process based on 0.2-0.3 tonne CO2 feedstock per tonne methanol 

Emission factors in this table are calculated from the feedstock consumption values in Table 3.13 based on the following feedstock 

carbon contents and heating values: 

 Natural Gas: 56 kg CO2/GJ 48.0 GJ/tonne 

 Oil: 74 kg CO2/GJ 42.7 GJ/tonne 

 Coal: 93 kg CO2/GJ 27.3 GJ/tonne 

 Lignite: 111 kg CO2/GJ 

Uncertainty values for this table are included in Table 3.27 

Sources: (a) Struker, A, and Blok, K, 1995; Methanex, 2003: (b) Hinderink, 1996: (c1 – c4) Lurgi, 2004a; Lurgi, 2004b; Lurgi, 2004c: 

(d) FgH-ISI, 1999 
Volume 3: Industrial Processes and Product Use 

3. 74 2006 IPCC Guidelines for National Greenhouse Gas Inventories 

TABLE 3.13 

METHANOL PRODUCTION FEEDSTOCK CONSUMPTION FACTORS

 GJ feedstock input /tonne methanol produced 

Process Configuration Feedstock Nat. gas Nat. gas + 

CO2

Oil Coal Lignite

Conventional Steam Reforming, without primary reforme (a) 

(Default Process and Natural Gas Default Feedstock) 

36.5 

Conventional Steam Reforming, with primary reformer (b) 33.4 29.3 

Conventional Steam Reforming, Lurgi Conventional process (c1) 31.4 

Conventional Steam Reforming, Lurgi Low Pressure Process (c2) 29.3 

Combined Steam Reforming, Lurgi Combined Process (c3) 31.6 

Conventional Steam Reforming, Lurgi Mega Methanol Process (c4) 30.1 

Partial oxidation process (d) 37.15 71.6 57.6 

Nat. gas + CO2 feedstock process based on 0.2-0.3 tonne CO2 feedstock per tonne methanol 

Sources: (a) Struker, A, and Blok, K, 1995; Methanex, 2003: (b) Hinderink, 1996: (c1 – c4) Lurgi, 2004a; Lurgi, 2004b; Lurgi, 2004c : 

(d) FgH-ISI, 1999 

Uncertainty values for this table are included in Table 3.27 

Methane emissions 

Methanex reported CH4 emissions from two Canadian methanol production plants in their 1996 Climate Change 

Action Plan (Methanex, 1996). Methanex reported that CH4 emissions from methanol production may arise from 

reformers, package boilers, methanol distillation units, and crude methanol storage tanks. CH4 emissions from 

the plants accounted for approximately 0.5 percent to 1.0 percent of the total greenhouse gas emissions from the 

plants, but were reported to vary depending upon the level of maintenance and operational control of the plant 

equipment. The average emission factor reported for two reporting years is 2.3 kg CH4 emissions per tonne of 

methanol produced. CH4 emissions from a second Methanex methanol production plant were reported to be 0.15 

kg CH4 per tonne of methanol produced. The higher of the two reported values, 2.3 kg CH4 per tonne of 

methanol produced, should be applied as the default CH4 emission factor for methanol production. CH4

emissions as low as 0.1 kg/tonne have been estimated for the methanol plant Tjeldbergodden, Norway (SFT, 

2003a). 

Ethylene 

Carbon dioxide emissions 

Emissions of CO2 from steam cracking for ethylene production may be estimated using the feedstock-specific 

emission factors in Table 3.14 and activity data for the amount of ethylene produced from the steam cracking 

processes. Separate emission factors are provided in Table 3.14 for the CO2 emissions from feedstock 

consumption and from supplemental energy consumption in the steam cracking process. However, the CO2

emissions from both feedstock consumption and supplemental energy consumption are to be reported as 

Industrial Process emissions under the reporting convention discussed above. The default emission factors are 

derived from plant-specific data for steam crackers operating in Western Europe. The emission factors may be 

adjusted by applying the default geographic adjustment factors in Table 3.15 to account for differences in the 

energy efficiency of steam cracking units among various countries and regions. Note that as indicated in Table 

3.11, the default feedstock for steam crackers operating in North and South America and Australia is ethane, and 

the default feedstock for steam crackers operating on other continents is naphtha. 

These default emission factors do not include CO2 emissions from flaring. Emissions from flaring amount to 

about 7 percent of total emissions in a well-maintained plant in Norway. Steam cracking processes that utilise 

naphtha, propane, and butane feedstocks are assumed to be energy neutral, requiring no use of supplemental fuel, 

therefore there are assumed to be no CO2 emissions associated with supplemental fuel consumption for these 

feedstocks. 
Chapter 3: Chemical Industry Emissions 

2006 IPCC Guidelines for National Greenhouse Gas Inventories 3.75 

TABLE 3.14 

STEAM CRACKING ETHYLENE PRODUCTION TIER 1 CO2 EMISSION FACTORS

 tonnes CO2/tonne ethylene produced 

Feedstock Naphtha Gas Oil Ethane Propane Butane Other 

Ethylene (Total Process and Energy Feedstock Use) 1.73 2.29 0.95 1.04 1.07 1.73 

 - Process Feedstock Use 1.73 2.17 0.76 1.04 1.07 1.73 

 - Supplemental Fuel (Energy Feedstock) Use 0 0.12 0.19 0 0 0 

Source: Neelis, M., Patel, M., and de Feber, M., 2003, Table 2.3, Page 26. 

Default feedstocks for ethylene production are identified in Table 3.11. The emission factors do not include supplemental fuel use in flares.

Other feedstocks are assumed to have the same product yields as naphtha feedstock. 

Uncertainty values for this table are included in Table 3.27. 

The emission factors in Table 3.14 may be used in the event that activity data are available only for the amount 

of ethylene produced by the steam cracking process. Steam cracking is a multi-product process that leads to 

ethylene, propylene, butadiene, aromatics, and several other high-value chemicals. There is an inherent 

assumption of a specific product mix in the default emission factors in Table 3.14. The default product mix for 

each emission factor in Table 3.14 is identified in the ethylene steam cracking feedstock-product matrix in 

Section 3.9.2.3. The feedstock/product matrix identifies the default values for production of ethylene, propylene, 

and other hydrocarbon products from the steam cracking process in units of kilograms of each product produced 

per tonne of feedstock. In order to develop the emission factors for steam cracking shown in Table 3.14 the total 

CO2 process emissions of a steam cracker have been divided by the output of ethylene only. In other words 

ethylene has been chosen as the reference for estimating the total CO2 emissions from the steam cracking process 

as a whole. Multiplication of the emission factors in Table 3.14 by the ethylene production therefore leads to the 

total CO2 emissions resulting not only from the production of ethylene but also from the production of propylene, 

butadiene, aromatics, and all other chemicals produced by the steam cracking process. The default emission 

factors in Table 3.14 provide the total CO2 emissions from the steam cracking process, not only the CO2 

emissions associated with the production of the ethylene from the steam cracking process. 

TABLE 3.15 

DEFAULT GEOGRAPHIC ADJUSTMENT FACTORS FOR TIER 1 CO2 EMISSION FACTORS FOR STEAM CRACKING ETHYLENE 

PRODUCTION

Geographic Region Adjustment Factor Notes 

Western Europe 100% Values in Table 3.14 are based on data from Western 

European steam crackers 

Eastern Europe 110% Not including Russia 

Japan and Korea 90% 

Asia, Africa, Russia 130% Including Asia other than Japan and Korea 

North America and South 

America and Australia 110% 

Source: Adjustment factors are based on data provided by Mr. Roger Matthews in personal communication to Mr. Martin Patel, May 2002. 

Uncertainty values for this table are included in Table 3.27. 

Methane emissions 

Default fugitive CH4 emission factors for steam cracking of ethane and naphtha for ethylene production are 

estimated from total VOC emissions factors and VOC species profile data from EMEP/CORINAIR Emission 

Inventory Guidebook (EEA, 2005). Overall volatile organic compound emissions from steam cracking are 

estimated to be 5 kg/tonne ethylene produced based on a European publication, for which the feedstock is 

assumed to be naphtha, and estimated to be 10 kg VOC/tonne ethylene produced based on a U.S. publication, for 

which the feedstock is assumed to be ethane. From the total VOC emission factors the overall CH4 emissions 

from steam cracking of naphtha are estimated from the VOC species profile to be 3 kg/tonne ethylene produced, 

primarily from leakage losses, and the overall CH4 emissions from cracking of ethane are estimated from the 

species profile to be twice those from cracking of naphtha (6 kg/tonne ethylene produced); however these factors 

are subject to uncertainty as the overall VOC emission factors of 5 kg VOC/tonne ethylene for naphtha feedstock 

and 10 kg VOC/tonne ethylene for ethane feedstock are each based on a single publication. Emissions of CH4
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3. 76 2006 IPCC Guidelines for National Greenhouse Gas Inventories 

from steam cracking of feedstocks other than ethane and naphtha have been assumed to be the same as that 

estimated from the EMEP/CORINAIR data for steam cracking of naphtha. 

Published data show a large variability in reported CH4 emission factors for ethylene production. The European 

Association of Plastics Manufacturers (APME) Eco-Profiles of the European Plastics Industry reports a CH4

emission factor for ethylene production of 2.9 kg CH4/tonne ethylene produced, as referenced in the APME EcoProfiles for Olefins Production (Boustead, 2003a). The CH4 emission factor for ethylene steam cracker process 

operations is based on life-cycle analysis data for 15 European steam crackers. Emissions as low as 0.14 kg 

CH4/tonne ethylene are estimated on the basis of direct measurement at a Norwegian ethylene plant (SFT 2003b) 

and as low as 0.03 kg CH4/tonne ethylene based on company data reported in the Australian Methodology for the 

Estimation of Greenhouse Gas Emissions and Sinks, 2003 (AGO, 2005). Other European and Australian steam 

cracker operators reported plant-specific CH4 emissions on the order of 10 percent of the values reported in 

Table 3.16 (DSM, 2002; Qenos, 2003; Qenos, 2005). Therefore, the emission factors in Table 3.16 should not be 

used to estimate CH4 emissions from steam cracker ethylene plants for which plant-specific data are available. 

In this case the plant-specific data and the Tier 3 method should be used. Default CH4 emission factors for 

various process feedstocks are shown in Table 3.16. Note that the default feedstocks for ethylene production are 

identified in Table 3.11. 

TABLE 3.16 

DEFAULT METHANE EMISSION FACTORS FOR ETHYLENE PRODUCTION 

Feedstock kg CH4/ tonne ethylene produced 

Ethane 6 

Naphtha 3 

All Other Feedstocks 3 

Source: EEA, 2005 (EMEP/CORINAIR Emission Inventory Guidebook) 

Uncertainty values for this table are included in Table 3.27. 

Ethylene dichloride and vinyl chloride monomer 

Carbon dioxide emissions 

Emission factors are provided in Table 3.17 for the ethylene dichloride and vinyl chloride monomer production 

processes, including the direct chlorination process, oxychlorination process, and balanced process. The CO2 

emission factors are derived by averaging plant-specific CO2 emissions data for European plants reported in the 

Integrated Pollution Prevention and Control (IPPC) Reference Document on Best Available Techniques in the 

Large Volume Organic Chemical Industry (European IPPC Bureau, February 2003; referred to in this section as 

the IPPC LVOC BAT Document). Note that as indicated in Table 3.11, the default process is the balanced 

process for EDC production with an integrated VCM production plant. The total CO2 emission factor for each 

process includes noncombustion CO2 emissions from the ethylene dichloride process vent and combustion CO2

emissions from ethylene dichloride plant combustion sources. Plant combustion source emission factors include 

combustion of both process waste gas and auxiliary fuel in the process waste gas thermal incinerator. The 

combustion-related emission factor does not include emissions from flares. Combustion-related emission factors 

in Table 3.17 are based on data from oxychlorination process plants but the emission factors are assumed also to 

apply to direct chlorination and balanced process plants. Feedstock consumption factors for ethylene dichloride 

and vinyl chloride monomer production processes are provided in Table 3.18. The PlasticsEurope EcoProfiles 

(Boustead, 2005) for EDC production indicates ethylene utilisation of 0.306 tonnes ethylene per tonne EDC 

produced, based on eight European plants. 

It should be noted that the CO2 emission factors in Table 3.17 in units of tonnes CO2 per tonne EDC produced 

and in units of tonnes CO2 per tonne VCM produced are not additive. The two CO2 emission factors both apply 

to the integrated EDC/VCM production process, however the tonnes CO2 per tonne EDC factor is based on EDC 

production activity data while the tonnes CO2 per tonne VCM factor is based on VCM production activity data. 

The CO2 emission factor that will be applied will depend upon whether activity data for EDC production or 

activity data for VCM production are available. Similarly, the feedstock consumption factors in Table 3.18 in 

units of tonnes ethylene consumed per tonne EDC produced and in units of tonnes ethylene consumed per tonne 

VCM produced are not additive. The feedstock consumption factor that will be applied will depend upon 

whether activity data are available for EDC production or for VCM production. 
Chapter 3: Chemical Industry Emissions 

2006 IPCC Guidelines for National Greenhouse Gas Inventories 3.77 

TABLE 3.17 

ETHYLENE DICHLORIDE/VINYL CHLORIDE PRODUCTION PROCESS TIER 1 CO2 EMISSION FACTORS 

Process Configuration tonne CO2/tonne EDC produced tonne CO2/tonne VCM produced 

Direct Chlorination Process 

Noncombustion Process Vent negligible emissions negligible emissions 

Combustion Emissions 0.191 0.286 

Total CO2 Emission Factor 0.191 0286 

Oxychlorination Process 

Noncombustion Process Vent 0.0113 0.0166 

Combustion Emissions 0.191 0.286 

Total CO2 Emission Factor 0.202 0.302 

Balanced Process [default process] 

Noncombustion Process Vent 0.0057 0.0083 

Combustion Emissions 0.191 0.286 

Total CO2 Emission Factor 0.196 0.294 

Values for CO2 emissions from EDC and VCM production for several European production plants were provided in Tables 12.6 and 

12.7 of the IPPC LVOC BAT Document (European IPPC Bureau, 2003). These values were averaged to calculate CO2 emission factors 

for EDC and VCM production. One EDC plant that is equipped with a CO2 control device and that reported zero CO2 emissions from 

the process is not included in the average emission factor. 

Source: European IPPC Bureau, 2003 (IPPC LVOC BAT Document, Tables 12.6 and 12.7 data). 

Uncertainty values for this table are included in Table 3.27. 

TABLE 3.18 

ETHYLENE DICHLORIDE/VINYL CHLORIDE MONOMER PROCESS TIER 1 FEEDSTOCK CONSUMPTION FACTORS 

Process Configuration tonne ethylene/tonne EDC 

produced 

tonne ethylene/tonne VCM 

produced 

Direct Chlorination Process 0.290 -- 

Oxychlorination Process 0.302 -- 

Balanced Process 0.296 0.47 

Source: European IPPC Bureau, 2003 (IPPC LVOC BAT Document, Section 12.3.1, Page 299-300, Section 12.1 Table 12.3, Page 293). 

Uncertainty values for this table are included in Table 3.27. 

Methane emissions 

The EMEP/CORINAIR ‘species profile’ for the ethylene dichloride/vinyl chloride monomer balanced process 

indicates that there are no CH4 emissions from the process other than CH4 emissions from combustion sources. 

The EMEP/CORINAIR species profile reports that VOC emissions from leakage losses and storage and 

handling do not contain CH4. The EMEP/CORINAIR also reports that 2 percent of the total VOC emissions 

from the balanced process are from combustion sources and that CH4 constitutes 1.2 percent of overall VOC 

emissions. Therefore it may be assumed that non-combustion CH4 emissions from ethylene dichloride/vinyl 

chloride monomer production are negligible. 

CH4 emissions from combustion of natural gas supplemental fuel in the ethylene dichloride/vinyl chloride 

monomer production process may be estimated from activity data for natural gas supplemental fuel consumption 

and CH4 emission factor for natural gas combustion. Natural gas consumption for integrated ethylene 

dichloride/vinyl chloride monomer production is estimated to be 110.1 Nm3 natural gas/tonne VCM produced for 

an integrated ethylene dichloride/vinyl chloride monomer production plant in the Netherlands and 126.4 Nm3 

natural gas/tonne VCM produced for an integrated ethylene dichloride/vinyl chloride monomer production plant 

in Germany. The average of these two values is 118.3 Nm3 natural gas/tonne VCM. The CH4 emission factor for 

the integrated EDC/VCM production process is based on a CH4 emission factor of 5 g CH4/GJ natural gas 

combusted and the average natural gas consumption of the two European plants. The default CH4 emission factor 

for the integrated ethylene dichloride/vinyl chloride monomer production process is provided in Table 3.19. The 
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3. 78 2006 IPCC Guidelines for National Greenhouse Gas Inventories 

default emission factor is not applicable to stand-alone EDC production plants. If natural gas consumption 

activity data are available, the CH4 emission factor of 5 g CH4/GJ may be applied directly to the activity data, 

rather than using the default emission factor. 

TABLE 3.19 

ETHYLENE DICHLORIDE/VINYL CHLORIDE PROCESS TIER 1 DEFAULT CH4 EMISSION FACTOR 

Process Configuration kg CH4/tonne VCM product produced 

Integrated EDC/VCM Production Plant 0.0226 

Sources: European IPPC Bureau, 2003 (IPPC LVOC BAT Document, Section 12.3.1, Table 12.4, Page 300); EEA, 2005 

(EMEP/CORINAIR Emission Inventory Guidebook, Processes in Organic Chemical Industries (Bulk Production) 1, 2-Dichloroethane 

and Vinyl Chloride (Balanced Process), Activity 040505, February 15, 1996, Section 3.4, Page B455-3, and Table 9.2, B455-5). 

Ethylene oxide 

Carbon dioxide emissions 

Emissions of CO2 from ethylene oxide production may be estimated using emission factors based on activity 

data for ethylene oxide production, and activity data for process configuration and catalyst selectivity. Separate 

CO2 emission factors are provided in Table 3.20 for the CO2 emissions from the air process and for the CO2

emissions from the oxygen process for a range of catalyst selectivity. The default emission factors for the air 

process and for the oxygen process are estimated from process-specific catalyst selectivity data provided in the 

IPPC LVOC BAT document. Specific data concerning the type of process and the selectivity of the process 

catalyst are needed in order to select emission factors from Table 3.20. The emission factors are derived from the 

catalyst selectivity using stoichiometric principles and are based on the assumption that emissions of CH4 and 

NMVOC from the process are negligible and that all of the carbon contained in the ethylene feedstock is 

converted either into ethylene oxide product or to CO2 emissions. The emission factors in Table 3.20 do not 

include emissions from flares. 

As shown in Table 3.20, the default emission factor for the air process is based on a default process catalyst 

selectivity of 70 percent and the default emission factor for the oxygen process is based on a default catalyst 

selectivity of 75 percent. If activity data are not available for the process configuration or the catalyst selectivity, 

the default process configuration is the air process and the default catalyst selectivity is 70 percent. If activity 

data are available that identify the process used as the oxygen process, but activity data are not for the catalyst 

selectivity for the oxygen process, the emission factor for the default catalyst selectivity of 75 percent for the 

oxygen process in Table 3.20 should be used. 

TABLE 3.20 

ETHYLENE OXIDE PRODUCTION FEEDSTOCK CONSUMPTION AND CO2 EMISSION FACTORS 

Process Configuration Catalyst 

Selectivity 

Feedstock Consumption 

(tonne ethylene/ 

tonne ethylene oxide) 

Emission Factor 

(tonne CO2/ 

tonne ethylene oxide) 

Default (70) 0.90 0.863 

Air Process [default process] 75 0.85 0.663 

80 0.80 0.5 

Default (75) 0.85 0.663 

Oxygen Process 80 0.80 0.5 

85 0.75 0.35 

Source: European IPPC Bureau, 2003 (IPPC LVOC BAT Document, Section 9.2.1, Page 224, Section 9.3.1.1, Page 231, Figure 9.6) 

Methane emissions 

The IPPC LVOC BAT document for ethylene oxide production reported CH4 emissions factors (in units of 

kilograms methane per tonne ethylene oxide produced) for the ethylene oxide process vent, ethylene oxide 

purification process exhaust gas steam, and fugitive emissions sources. CH4 emission factors were reported in 

the IPPC LVOC BAT document for European ethylene oxide plant carbon dioxide removal vents before and 

after treatment. CH4 emissions were also reported for two ethylene oxide plants in the Netherlands. CH4

emission factors for ethylene oxide production were developed by averaging these data. Emissions of CH4 may 

be estimated by applying the emissions factors included in Table 3.21 to activity data for ethylene oxide 

production. The default CH4 emission factor for ethylene oxide production assumes no thermal treatment process. 
Chapter 3: Chemical Industry Emissions 

2006 IPCC Guidelines for National Greenhouse Gas Inventories 3.79 

TABLE 3.21 

ETHYLENE OXIDE PRODUCTION TIER 1 CH4 EMISSION FACTORS

Process Configuration kg CH4/tonne ethylene oxide produced 

No Thermal Treatment [default factor] 1.79 

Thermal Treatment 0.79 

Source: European IPPC Bureau, 2003 (IPPC LVOC BAT Document, Table 9.6, Page 233; Table 9.8, Page 236; Table 9.9, Page 236). 

Acrylonitrile 

Carbon dioxide emissions 

Process vent CO2 emissions from the acrylonitrile production process by the direct ammoxidation of propylene 

may be calculated from acrylonitrile production activity data using the emission factors provided in Table 3.22: 

TABLE 3.22 

ACRYLONITRILE PRODUCTION CO2 EMISSION FACTORS

Process Configuration 

Direct Ammoxidation of Propylene 

tonnes CO2/tonne acrylonitrile produced 

Secondary Products Burned for Energy Recovery/Flared (default) 1.00 

Acetonitrile Burned for Energy Recovery/Flared 0.83 

Acetonitrile and Hydrogen Cyanide Recovered as Product 0.79 

Source: European IPPC Bureau, 2003 (IPPC LVOC BAT Document, Section 11.3.1.1, Table 11.2, Page 274 and Section 11.3.1.2, Page 

275) 

The emission factors in Table 3.22 are based on an average (default) propylene feedstock consumption factor of 

1.09 tonnes propylene feedstock per tonne acrylonitrile produced, corresponding to a primary product yield 

factor of approximately 70 percent. The default CO2 emission factor is based on conversion of propylene 

feedstock to secondary product acetonitrile at 18.5 kilograms per tonne acrylonitrile produced, and conversion of 

propylene to secondary product hydrogen cyanide at 105 kilograms per tonne acrylonitrile produced, and is 

based on process-specific acrylonitrile yield data and process-specific feedstock consumption data reported in 

the IPPC LVOC BAT document (European IPPC Bureau, 2003). Note however that the acrylonitrile production 

process may be configured and operated to produce a greater or lesser amount of secondary products. The 

default CO2 emission factor is based on the assumption that the secondary products (acetonitrile and hydrogen 

cyanide) of the acrylonitrile production process and hydrocarbon by products in the main absorber vent gas are 

either burned for energy recovery or flared to CO2 and are not recovered as products or emitted to the 

atmosphere without combustion treatment. The CO2 emission factors do not include CO2 emissions from any 

combustion of auxiliary fuel (e.g., natural gas) for the process waste gas energy recovery or flare systems. 

If activity data are not available concerning whether secondary products are recovered for sale, the default 

assumption is that the secondary products are either burned for energy recovery or flared to CO2 and the default 

primary product process yield factor is 70 percent. 

For the process configuration where secondary products (acetonitrile and hydrogen cyanide) are recovered for 

sale and are not either flared to CO2 or burned for energy recovery, the overall process yield factor of primary 

and secondary products is 85 percent. 

If activity data for propylene feedstock consumption are not available, the propylene feedstock consumption may 

be estimated from the acrylonitrile production activity data by applying a default feedstock consumption factor 

of 1.09 tonnes propylene feedstock consumed per tonne acrylonitrile produced. 

Methane emissions 

The Life-Cycle Analysis Data Summary for Acrylonitrile reports a CH4 emission factor for acrylonitrile 

production of 0.18 kg CH4/tonne acrylonitrile produced, as referenced in the European Association of Plastics 

Manufacturers (APME) Life-Cycle Analysis Report (Boustead, 1999). The CH4 emission factor for acrylonitrile 

process operations is based on life-cycle analysis data for European acrylonitrile plants in Germany, Italy, and 

the United Kingdom collected between 1990 and 1996. CH4 emissions from acrylonitrile production may be 

estimated by applying this default emission factor to the acrylonitrile production data. 
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3. 80 2006 IPCC Guidelines for National Greenhouse Gas Inventories 

Carbon black 

Carbon dioxide emissions 

Emissions of CO2 from carbon black production may be estimated by applying the process and feedstockspecific emission factors to the carbon black production activity data. Separate emission factors are provided in 

Table 3.23 for the furnace black process, thermal black process, and acetylene black process and their associated 

feedstocks, and separate emission factors are provided for primary feedstock and secondary feedstock. The 

emission factors are based on the assumption that process emissions are subjected to a thermal treatment process. 

A range of values for primary and secondary carbon black feedstock is included in Table 4.11 of the draft 

Integrated Pollution Prevention and Control (IPPC) Reference Document for Best Available Techniques in the 

Large Volume Inorganic Chemicals (LVIC) Solid and Others Industry (European IPPC Bureau, June 2005; 

referred to in this chapter as the Draft IPPC LVIC BAT Document.) The CO2 emission factors in Table 3.23 are 

based on the average of the range of values. Primary and secondary feedstock consumption is converted to 

carbon consumption using average values for carbon black feedstock carbon content. The CO2 emission factors 

are calculated from the carbon input to the process (primary and secondary feedstocks) and carbon output 

(carbon black) from the process, using an average value for carbon black carbon content. 

TABLE 3.23 

CARBON BLACK PRODUCTION TIER 1 CO2 EMISSION FACTORS

tonnes CO2/tonne carbon black produced 

Process Configuration Primary Feedstock Secondary Feedstock Total Feedstock 

Furnace Black Process (default process) 1.96 0.66 2.62 

Thermal Black Process 4.59 0.66 5.25 

Acetylene Black Process 0.12 0.66 0.78 

Source: European IPPC Bureau, 2005 (Draft IPPC LVIC BAT Document, Table 4.11 data) 

Methane emissions 

CH4 emissions for the carbon black production process are provided in Table 3.24. The draft IPPC LVIC BAT 

document for carbon black reported the CH4 content of uncombusted tail gas from the carbon black production 

process and the estimated rate of generation of tail gas from the carbon black production process. Based on 

10,000 Nm3

 tail gas per tonne carbon black produced and an average reported CH4 concentration of 0.425 

percent by volume, the uncontrolled CH4 emission factors is 28.7 kg CH4/tonne carbon black produced. 

Combustion flare efficiency for carbon black process flare systems was reported in the Draft IPPC LVIC BAT 

Document as 99.8 percent for carbon monoxide, and the same efficiency is assumed to apply to CH4. The CH4

emission factor for carbon black production after application of combustion control is 0.06 kg CH4/tonne carbon 

black produced. An overall CH4 emission factor of 0.11 kg CH4/tonne carbon black, based on company data, was 

reported in the Australian Methodology for the Estimation of Greenhouse Gas Emissions and Sinks, 2003 (AGO, 

2005.) Three carbon black production plants in Germany reported a common CH4 emission factor of 0.03 kg 

CH4/tonne carbon black produced, based on measurement data after waste gas combustion using BAT 

(Thermische Nachverbrennung als Stand der Technik.) 

TABLE 3.24 

CARBON BLACK PRODUCTION TIER 1 CH4 EMISSION FACTORS

Process Configuration kilogram CH4/tonne carbon black produced 

(Carbon Black Process Tail Gas )

No Thermal Treatment 28.7 

Thermal Treatment (default process) 0.06 

Source: European IPPC Bureau, 2005 (Draft IPPC LVIC BAT Document, Table 4.8, Page 209; Table 4.10, 

Page 213, Section 4.3.2.3, Page 210). 

TIER 2 

The Tier 2 methodology is based on mass balance calculations and therefore there are no emission factors 

associated with the methodology. 
Chapter 3: Chemical Industry Emissions 

2006 IPCC Guidelines for National Greenhouse Gas Inventories 3.81 

TIER 3 

For the Tier 3 method plant specific emissions may be estimated using Equations 3.20 through 3.22 for CO2, and 

using either Equation 3.26 or Equations 3.27 through 3.29 for CH4. The emission factors may be related to 

annual production for estimation of emissions between measurements when these are not continuous. 

3.9.2.3 CHOICE OF ACTIVITY DATA

General aspects of data collection for obtaining activity data are discussed in Chapter 2 of Volume 1. When 

using the Tier 3 method plant-specific activity data should be obtained from the production plants. Direct 

measurements of the total flow to the steam cracker and flare system together with an analysis of the gas carbon 

content will provide the most accurate basis for an emissions estimate. 

Plant specific energy balance and/or carbon balance may also be used to derive plant specific emission factors. 

The variety of energy and carbon flows across the plant boundary makes this a data intensive but still much less 

resource intensive approach. While feedstock consumption data may be hard to obtain sales data and national 

statistics may provide approximate production volumes of the chemicals. 

METHANOL 

Emissions of CO2 from methanol production may be calculated from specific feedstock (e.g., natural gas) 

consumption and product (methanol) production activity data and carbon mass balance calculations. 

ETHYLENE 

Emissions of CO2 from ethylene production may be calculated from specific feedstock consumption and product 

production activity data and carbon mass balance calculations. In order to create a complete mass balance for the 

ethylene production process and implement the Tier 2 methodology for ethylene production, all feedstocks and 

the production and disposition of all primary and secondary products of the process should be identified using 

activity data. In cases where activity data are available for ethylene production but not available for production 

of secondary products from the steam cracking process, the production of secondary products may be estimated 

using the default factors in Table 3.25 and Equation 3.18. However, use of these default factors is a less accurate 

method than use of specific activity data for all primary and secondary products, and will increase the 

uncertainty of the estimate, as performance of steam crackers may vary depending on site-specific conditions. 

For example, site-specific data reported for steam crackers operating in Germany indicate that hydrocarbon 

losses under normal operating conditions are on the order of 8.5 kg per tonne of hydrocarbon feedstock (BASF, 

2006) whereas the default value for hydrocarbon losses shown in Table 3.25 is 5 kg per tonne of hydrocarbon 

feedstock. In the event that activity data are not available for all secondary products, the Tier 1 method can be 

applied instead of the Tier 2 method. 

Secondary products produced by the steam cracking process may recovered and transferred to a petrochemical 

plant or petroleum refinery for material reuse, recycled within the steam cracking process as feedstock, or burned 

for energy recovery. Typically C4+ secondary products are recycled as feedstock or recovered for material reuse 

(BASF, 2006). Allocation of CO2 emissions from combustion of secondary products for energy recovery is 

described in Box 1.1 in Chapter 1 of this volume. If activity data are not available for the disposition of C4+ 

secondary products the default assumption is that the C4+ secondary products are recovered and transferred to 

another process for material reuse. If data are not available for the disposition of CH4 produced by the steam 

cracking process, the default assumption is that the CH4 is burned for energy recovery within the steam cracking 

process and results in CO2 emissions from the process. 

Steam crackers operated within the petrochemical industry may obtain the petrochemical feedstock for the 

ethylene production process directly from an adjacent petroleum refinery. Depending upon the feedstock and 

process operating conditions, steam crackers may also generate ‘backflows’ of hydrocarbon by-products that are 

returned to the adjacent refinery for further processing. Any CO2 emissions from processing backflows at 

petroleum refineries are not included in the process CO2 emission factors for the steam cracker ethylene 

production process, but are considered in the feedstock and carbon flow analysis for the process. 
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3. 82 2006 IPCC Guidelines for National Greenhouse Gas Inventories 

TABLE 3.25 

ETHYLENE STEAM CRACKING FEEDSTOCK-PRODUCT MATRIX

 kg product/tonne feedstock 

Product Feedstock Naphtha Gas oil Ethane Propane Butane Others 

High Value Chemicals 645 569 842 638 635 645 

Ethylene 324 250 803 465 441 324 

Propylene 168 144 16 125 151 168 

Butadiene 50 50 23 48 44 50 

Aromatics 104 124 0 0 0 104 

Fuel grade products and backflows 355 431 157 362 365 355 

Hydrogen 11 8 60 15 14 11 

Methane 139 114 61 267 204 139 

Ethane and propane after recycle 0 0 0 0 0 0 

Other C4 62 40 6 12 33 62 

C5/C6 40 21 26 63 108 40 

C7+ non-aromatics 12 21 0 0 0 12 

<430C 52 26 0 0 0 52 

>430C 34 196 0 0 0 34 

Losses 5 5 5 5 5 5 

Total 1 000 1 000 1 000 1 000 1 000 1 000 

Source: Neelis, M; Patel, M; de Feber, M; Copernicus Institute, April 2003, Table 2.2, Page 24 

ETHYLENE DICHLORIDE AND VINYL CHLORIDE MONOMER 

Emissions of CO2 from ethylene dichloride and vinyl chloride monomer production may be calculated from 

specific feedstock (ethylene) consumption and product (ethylene dichloride) production activity data and carbon 

mass balance calculations. 

ETHYLENE OXIDE 

Emissions of CO2 from ethylene oxide production may be calculated from specific feedstock (ethylene) 

consumption and product (ethylene oxide) production activity data and carbon mass balance calculations. 

ACRYLONITRILE 

In the event that activity data are not available for production of secondary products (acetonitrile and hydrogen 

cyanide), the default values in Table 3.26 and Equation 3.19 may be applied to the activity data for primary 

product production to estimate secondary product production. 

TABLE 3.26

SECONDARY PRODUCT PRODUCTION FACTORS FOR ACRYLONITRILE PRODUCTION PROCESS

Secondary Product kg secondary product/tonne acrylonitrile produced 

Acetonitrile 18.5 

Hydrogen Cyanide 105 

Note: The secondary product production factors in this table are based on acrylonitrile production from propylene feedstock. In the 

event that feedstocks other than propylene are used, the factors in this table would not apply. Process-specific factors would need to be 

developed in order to apply the Tier 2 mass balance approach to acrylonitrile production from feedstocks other than propylene. 

Source: European IPPC Bureau, 2005 (IPPC LVOC BAT Document, Section 11.3.4, Page 27) 

If no activity data are available concerning acetonitrile product recovery it may be assumed that it is not 

recovered as product and is burned for energy recovery to CO2. If no activity data are available concerning 

thermal treatment of the acetonitrile main absorber vent gas it may be assumed that the vent gas is thermally 

treated and combusted to CO2 and is not vented to the atmosphere uncontrolled. 
Chapter 3: Chemical Industry Emissions 

2006 IPCC Guidelines for National Greenhouse Gas Inventories 3.83 

CARBON BLACK 

Emissions of CO2 from carbon black production may be calculated from specific primary feedstock (e.g., carbon 

black feedstock) and secondary feedstock (e.g., natural gas) consumption and product (carbon black) production 

activity data and carbon mass balance calculations. 

3.9.2.4 COMPLETENESS

In estimating CO2 emissions from petrochemical and carbon black processes, there is a risk of double-counting 

or omission in either the IPPU or the Energy Sector. Petrochemical and carbon black plants produce methane 

and non-methane hydrocarbon by-products that may be burned for energy recovery and such energy recovery 

may be reported in national energy statistics under ‘other’ fuels or some similar categorisation. If CO2 emissions 

from ‘other’ fuel combustion include industrial process off gases that are burned for energy recovery some 

adjustment to the energy statistics or to the CO2 emissions calculation for petrochemical production would be 

needed to avoid double counting of the CO2 emissions. 

METHANOL 

There may be production of methanol from biogenic (renewable) sources. Such biogenic methanol may be 

incorporated into methanol national production statistics, which would result in overestimation of CO2 emissions 

from fossil fuel (e.g., natural gas) derived methanol unless adjustments are made to the methanol production 

activity data. 

ETHYLENE 

There may be production of ethylene from petroleum refining processes or from petrochemical processes other 

than steam crackers. Such ethylene may be incorporated into ethylene national production statistics, which 

would result in overestimation of CO2 emissions from steam cracker derived ethylene unless adjustments are 

made to the ethylene production activity data. 

ETHYLENE DICHLORIDE AND VINYL CHLORIDE MONOMER 

Ethylene dichloride is an intermediate petrochemical product used to manufacture vinyl chloride monomer and 

other products. Activity data for production of ethylene dichloride may not be complete because the ethylene 

dichloride may be converted directly to vinyl chloride monomer in an integrated EDC/VCM plant. Therefore it 

may be the case that the vinyl chloride monomer production activity data are more complete with respect to 

industry coverage than the ethylene dichloride production activity data. However, utilisation of vinyl chloride 

monomer activity data as a surrogate for ethylene dichloride data also has issues related to completeness because 

not all of the ethylene dichloride is used to manufacture vinyl chloride monomer. Therefore adjustments to the 

activity data for vinyl chloride monomer may be needed to account for utilisation of ethylene dichloride in the 

production of other products. Based on data for North America and Europe utilisation of ethylene dichloride for 

products other than vinyl chloride monomer would amount to the order of 5 percent of total ethylene dichloride 

production. 

ETHYLENE OXIDE 

Ethylene oxide is an intermediate petrochemical product used to manufacture ethylene glycols and other 

products. Activity data for production of ethylene oxide may not be complete because the ethylene oxide may be 

converted directly to ethylene glycol in an integrated EO/EG plant. Ethylene oxide may also be converted into 

other products (e.g., amines, ethers, etc.) in integrated plants. Since only on the order of 70 percent of ethylene 

oxide production worldwide is used in the manufacture of ethylene glycols, production activity data for chemical 

products of ethylene oxide may not be more complete with respect to industry coverage than the ethylene oxide 

production activity data. 

CARBON BLACK 

There may be small amounts of production of carbon black from biogenic (renewable) sources such as animal 

black and bone black. Such biogenic carbon black may be incorporated into carbon black national production 

statistics, which would result in overestimation of CO2 emissions from fossil fuel derived carbon black. There 

also may be carbon black production within the physical boundaries of petroleum refineries rather than within 

the chemical industry. Carbon black produced within petroleum refineries is anticipated to be incorporated into 

national carbon black production statistics, therefore CO2 emissions from carbon black production within 

petroleum refineries should be reported along with other emissions from carbon black production within the 

chemical industry as industrial process emissions. 

There may be gaps in completeness with respect to carbon black feedstock consumption activity data. Activity 

data for carbon black feedstock derived from coal tar products, waste gases, or acetylene may not be available, 
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3. 84 2006 IPCC Guidelines for National Greenhouse Gas Inventories 

which would result in underestimating of CO2 emissions from carbon black production if a higher-tier carbon 

balance approach was used. 

3.9.2.5 DEVELOPING CONSISTENT TIME SERIES

The emissions from petrochemical and carbon black production should be estimated using the same Tier and 

type of activity data for all years. Constructing a time series for emissions from petrochemical and carbon black 

production using plant specific measurement activity data will give the most accurate current emissions. 

However activity data on flaring and fugitive emissions will most likely not be available for previous years. If no 

technology upgrades have taken place calculating a plant specific emission factor based on recent measurement 

data related to production of petrochemicals may provide a reasonable result. Petrochemical production is often 

integrated in an industrial complex producing more than one chemical, or exchanges energy or chemical flows 

with adjacent industrial plants, and carbon black may be produced within petroleum refineries. When 

constructing a time series based on feedstock consumption great care should be taken to assure that the activity 

data includes the same flows every year in the time series. Again a Tier 1 type calculation using emission factors 

developed from recent plant specific emission estimates based on Tier 2 carbon balance calculation may be used. 

Investigations to uncover a change in choice of feedstock as well as variations in primary and secondary 

chemicals produced both within a single year and between years. Reconstruction of gaps in emission estimates 

and recalculations should follow the guidance in Volume 1, Chapter 5. 

3.9.3 Uncertainty assessment 

Uncertainty assessments for each emissions factor and activity data applicable to each process are discussed in 

this section. Uncertainty ranges for the emission factors and activity data included in the Tables in the previous 

sections are summarised in Table 3.27. 

METHANOL 

Much of the uncertainty in emission estimates for methanol production is related to the difficulty in determining 

activity data including the quantity of methanol produced and, for higher tier methodologies, the amount of 

natural gas and other feedstocks consumed on an annual basis. Natural gas and other feedstock consumption may 

only be reported on an annual basis in national energy statistics, without any breakout of consumption for 

methanol production. If natural gas consumption activity data are not available then only an emission factor 

approach rather than a higher tier carbon balance approach is applicable. If activity data are not available for 

consumption of other feedstocks for methanol production, it may be assumed that all of the national methanol 

production is from natural gas feedstock. However, this assumption would introduce some uncertainty. Further, 

activity data may not be available for annual CO2 feedstock consumption in methanol production plants that 

utilise CO2 as a supplemental feedstock in the production process. 

ETHYLENE 

Uncertainty in activity data for ethylene production is related to the difficulty in determining the types, quantities, 

and characteristics of feedstocks to the steam cracking process (e.g., ethane, naphtha) and the types, quantities, 

and characteristics of products from the process (e.g., ethylene, propylene). Feedstock consumption and product 

production may only be reported on an annual basis in national energy statistics and commodity statistics, 

without any breakout of feedstock consumption for ethylene production or product production from the steam 

cracking ethylene production process. The ability to conduct a carbon balance calculation for ethylene 

production depends upon the availability of both activity data for consumption of specific feedstocks and 

production of specific products of the steam cracking process. If only activity data for national annual ethylene 

production are available, the default feedstock for the country/region may be assumed and the default emission 

factor applied. In this case the feedstocks analysis would be conducted by utilising the default yield table for the 

default feedstock. However, considering the wide variability in emission factors and yield factors among the 

feedstocks, the unavailability of specific feedstock consumption data would introduce significant uncertainty into 

the emissions calculations and feedstocks analysis. If specific feedstock consumption activity data are available 

then a separate emissions estimate and feedstocks analysis may be conducted for each feedstock, which would 

reduce the uncertainty. Ideally, however, activity data would be available for both specific feedstock 

consumption and specific product production, allowing a higher tier carbon balance calculation to be conducted. 

Another source of uncertainty is related to the difficulty in determining other details of the steam cracking 

ethylene process configuration, including backflows of products of the steam cracking process from the 

petrochemical plant to the [potentially adjacent] petroleum refinery and flows of by products to energy recovery 

or flaring. The unavailability of activity for refinery backflows would introduce uncertainty into the feedstocks 

analysis. 
Chapter 3: Chemical Industry Emissions 

2006 IPCC Guidelines for National Greenhouse Gas Inventories 3.85 

ETHYLENE DICHLORIDE AND VINYL CHLORIDE MONOMER 

Sources of uncertainty for ethylene dichloride include the difficulty in determining the specific process utilised 

for the ethylene dichloride production and in determining activity data for the consumption of ethylene feedstock 

in the production process. If only activity data for ethylene dichloride production are available, the emission 

calculation may be conducted using the default [balanced] process product yield factor and default emission 

factor for the process. However, considering the variability in emission factors and yield factors for the 

oxychlorination process, direct oxidation process, and balanced process, the unavailability of specific ethylene 

feedstock consumption data by process would introduce significant uncertainty into the emissions calculations 

ETHYLENE OXIDE 

A main source of uncertainty for ethylene oxide production is the difficulty in determining activity data for the 

consumption of ethylene feedstock for ethylene oxide production. If ethylene consumption activity data are not 

available then only an emission factor approach rather than a higher tier carbon balance approach is applicable. 

If only activity data for national annual ethylene oxide production are available, the default product yield may be 

assumed and the default emission factor applied. In this case the feedstocks analysis would be conducted by 

utilising the default product yield factor. However, considering the range of reported product yield factors and 

emission factors for the ethylene oxide process, the unavailability of specific ethylene feedstock consumption 

data would introduce significant uncertainty into the emissions calculations. 

ACRYLONITRILE 

Sources of uncertainty for acrylonitrile production include the difficulty in determining the specific process 

configuration for acrylonitrile production, in determining activity data for the consumption of propylene 

feedstock in the production process, and in determining activity data for the production of acrylonitrile and 

acetonitrile from the process. If only activity data for acrylonitrile production are available, the emission 

calculation may be conducted using the default process configuration (assuming no acetonitrile recovery) and 

default emission factor for the process. However, the assumption that acetonitrile is not recovered from the 

process introduces significant uncertainty in the emission and feedstocks calculations and may result in 

overestimation of emissions and underestimation of feedstocks flows from the acrylonitrile process. Activity 

data for national production of both acrylonitrile and acetonitrile from the acrylonitrile production process would 

allow application of the process-specific emission factor for the percentage of national acrylonitrile production 

from which acetonitrile is recovered. Ideally, however, activity data for propylene consumption and activity data 

for acrylonitrile, acetonitrile, and hydrogen cyanide production from the acrylonitrile production process would 

allow utilisation of a higher-tier method, which would reduce the uncertainty. 

CARBON BLACK 

Uncertainty in activity data for carbon black production is related to the difficulty in determining the types, 

quantities, and characteristics of primary and secondary feedstocks to the carbon black process, and in 

determining the type of process used for the carbon black production and the characteristics of the carbon black 

product from the process. Primary and secondary feedstock consumption and carbon black production may only 

be reported on an annual basis in national energy statistics and commodity statistics, without any breakout of 

feedstock consumption for carbon black production for each carbon black production process. Most worldwide 

production of carbon black is by the furnace black process, therefore if feedstock consumption activity data are 

not available by process, all of the carbon black production may be assumed to be from the furnace black process 

without introducing a large amount of uncertainty. 

Also, if activity data are available for primary carbon black feedstock consumption, the data may be reported in 

generic terms as ‘carbon black feedstock’ without any indication of whether the feedstock is a petroleum-based 

feedstock produced at petroleum refineries or a coal tar-based feedstock produced from metallurgical coke 

production. Activity data may also not be available for other primary carbon black feedstocks (e.g., acetylene). 

Also, specific activity data may be available for natural gas consumption as secondary carbon black feedstock, 

however, activity data may not be available for other secondary feedstocks that may be used in carbon black 

production (e.g., coke oven gas). Unavailability of specific primary and secondary feedstock consumption data 

would add uncertainty to the feedstocks analysis. 

The ability to conduct a carbon balance calculation for carbon black production depends upon the availability of 

activity data for the consumption and the characteristics of primary and secondary feedstocks. If only activity 

data for national annual carbon black production are available, the default feedstock characteristics and product 

yield may be assumed and the default emission factor may be applied. However, considering the variability in 

feedstock characteristics and origin, the unavailability of specific feedstock consumption and composition 

activity data would introduce significant uncertainty into the emissions and feedstocks calculations. If specific 

feedstock consumption and characteristics activity data and associated carbon black production activity data are 
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3. 86 2006 IPCC Guidelines for National Greenhouse Gas Inventories 

available then a separate carbon balance and feedstocks analysis may be conducted for each feedstock and 

process using a higher tier method, which would reduce the uncertainty. 

UNCERTAINTY RANGES 

Uncertainty ranges for Tier 1 emission factors and Tier 2 activity data and Tier 3 activity data for each process 

are provided in Table 3.27. The source of the data or expert judgement used in preparing the uncertainty estimate 

is identified in the table for each factor or activity data. Expert judgement elicitation was conducted by 

evaluating the range of available data. In many cases process-specific data were available only for several plants; 

the relatively large uncertainty ranges are the result of the relatively few data available and the expected 

variability of process configurations and feedstock utilisation efficiency among petrochemical and carbon black 

plants. 

TABLE 3.27 

UNCERTAINTY RANGES FOR EMISSION FACTORS AND ACTIVITY DATA 

Method Reference Factor Uncertainty Range Source 

Tier 3 Direct measurement of fuel 

consumption together with gas 

composition samples for all 

substances 

- 5 to + 5 % Expert judgement by Lead 

Authors of Section 3.9, on the 

basis of discussions with 

national industry January 2005. 

Tier 1 Table 3.12 Methanol production CO2

emission factors 

-30% to +30% Expert judgement by Lead 

Authors of Section 3.9. 

Tier 1 Table 3.13 Methanol Production Feedstock 

Consumption Factors 

-30% to +30% Expert judgement by Lead 

Authors of Section 3.9. 

Tier 1 Methane Emission Factor for 

Methanol Production 

-80% to +30% Expert judgement by Lead 

Authors of Section 3.9 on the 

basis of Methanex plant data. 

Tier 1 Table 3.14 Ethylene Production CO2

Emission Factors 

-30% to +30% IPPC LVOC BAT Document, 

Figure 7.10, 

Tier 1 Table 3.15 Geographic Adjustment Factors 

For CO2 Emissions Factors For 

Ethylene Production 

-10% to +10% Expert judgement by Lead 

Authors of Section 3.9. 

Tier 1 Table 3.16 Methane Emission Factors for 

Ethylene Production 

-10% to +10% Expert judgement by Lead 

Authors of Section 3.9. 

Tier 1 Table 3.17 Ethylene Dichloride/Vinyl 

Chloride Production Process 

Vent CO2 Emission Factors 

-20% to +10% IPPC LVOC BAT Document, 

Tables 12.6 and 12.7 

Tier 1 Table 3.17 Ethylene Dichloride/Vinyl 

Chloride Production CO2

Emission Factors 

-50% to +20% IPPC LVOC BAT Document, 

Tables 12.6 and 12.7 

Tier 1 Table 3.18 Ethylene Dichloride/Vinyl 

Chloride Monomer Process 

Feedstock Consumption 

Factors 

-2% to +2% IPPC LVOC BAT Document, 

Section 12.3.1, Page 300 

Tier 1 Table 3.19 Ethylene Dichloride/Vinyl 

Chloride Monomer Process 

CH4 Emission Factors 

-10% to +10% IPPC LVOC BAT Document, 

Section 12.3.1, Table 12.4, Page 

300 

Tier 1 Table 3.20 Ethylene Oxide Production 

Feedstock Consumption and 

CO2 Emission Factors 

-10% to +10% Expert judgement by 

Lead Authors of Section 3.9. 

Tier 1 Table 3.21 Ethylene Oxide Production 

CH4 Emission Factors 

-60% to +60% IPPC LVOC BAT Document, 

Table 9.6, Page 233; Table 9.8, 

Page 236; Table 9.9, Page 236 

Tier 1 Table 3.22 Acrylonitrile Production CO2

Emission Factors 

-60% to +60% IPPC LVOC BAT Document, 

Section 11.3.1.1, Table 11.2, 

Page 274. 
Chapter 3: Chemical Industry Emissions 

2006 IPCC Guidelines for National Greenhouse Gas Inventories 3.87 

TABLE 3.27 (CONTINUATION) 

UNCERTAINTY RANGES FOR EMISSION FACTORS AND ACTIVITY DATA 

Method Reference Factor Uncertainty Range Source 

Tier 1 Acrylonitrile Production CH4

Emission Factors 

-10% to +10% Boustead, 2003b (Eco-Profiles 

of the European Plastics 

Industry Methodology I. 

Boustead, Report prepared for 

APME, July 2003, Page 40) 

Tier 1 Table 3.23 Carbon Black Production CO2

Emission Factors 

-15% to +15% Draft IPPC LVIC BAT 

Document, Table 4.11, Page 214 

Tier 1 Table 3.24 Carbon Black Production CH4

Emission Factors 

-85% to +85% Draft IPPC LVIC BAT 

Document, Table 4.8, Page 209 

Tier 2 Table 3.25 Ethylene Steam Cracking 

Feedstock-Product Matrix 

-10% to + 10% Expert judgement by Contributing 

Authors of Section 3.9 

Tier 2 Table 3.26 Secondary Product Production 

Factors for Acrylonitrile 

Production Process 

-20% to +20% Expert judgement by Lead 

Authors of Section 3.9. 

3.9.4 Quality Assessment/Quality Control (QA/QC), 

Reporting and Documentation 

3.9.4.1 QUALITY ASSESSMENT/QUALITY CONTROL

Quality Assurance/Quality Control for emissions factors and activity data involves methods to improve the 

quality or better understand the uncertainty of the emissions estimates. It is good practice to conduct quality 

control checks for the Tier 1 method as outlined in Volume 1, Chapter 6. More extensive quality control checks 

and quality assurance procedures are applicable, if Tier 2 or Tier 3 methods are used to determine emissions. 

Inventory compilers are encouraged to use higher tier QA/QC for key categories as identified in Volume 1, 

Chapter 4. 

Evaluation of Tier 1 and Tier 2 method activity data 

The Tier 1 and Tier 2 methods both depend upon the application of activity data for petrochemical and carbon 

black production and/or activity data for feedstock consumption. These activity data should not be expected to 

vary by more than about +/- 10 percent year to year, barring significant changes in the overall economic output 

of the country, the construction of new petrochemical production capacity, or other similar factors. If the 

activity data vary by more than about +/-10 percent year to year, it is good practice to assess and document the 

country-specific conditions that account for the differences. 

Evaluation of Tier 1 method emission factors 

Inventory compilers that develop country-specific emission factors for petrochemical and carbon black 

production and apply the Tier 1 method should assess whether the estimated emission factors are within the 

range of the default emission factors and process-specific emission factors provided for the Tier 1 method in this 

guidance. If the emission factors are outside of the range of factors reported in this Guidance, then the reasons 

why this is the case should be investigated (e.g., the process configuration differs from that for the emission 

factors reported in this guidance; the feedstock is a unique material not considered in this Guidance.) Inventory 

compilers should also ensure that the country-specific emission factors are consistent with the values derived 

from analysis of the process chemistry. For example, for methanol production from natural gas the carbon 

content of the CO2 generated, as estimated using the emission factor, should equal approximately the difference 

between the carbon content of the natural gas feedstock and the carbon content of the methanol product. If the 

emission factors are outside of the estimated ranges, it is good practice to assess and document the plant-specific 

conditions that account for the differences. It is also good practice or inventory compilers using Tier 1 method 

emission factors included in this Guidance to conduct quality control checks to assess whether the data 

characteristics of the emission factor conform to the characteristics of the petrochemical and carbon black 

production processes in the country in which the emission factor is applied. 
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3. 88 2006 IPCC Guidelines for National Greenhouse Gas Inventories 

Evaluation of Tier 2 method mass balance calculations 

Application of the Tier 2 mass balance method depends upon the identification and characterisation of process 

flows. For the Tier 2 method, failure to identify all carbon-containing process flows or mischaracterisation of the 

flow rates or carbon contents of such process flows could result in significant deviation of the estimated CO2

emissions from the actual CO2 emissions. The quality of Tier 2 mass balance calculation results are generally 

more dependent upon the quality of the activity data than are Tier 1 calculation results because in general a 

greater number of activity data need to be applied to the Tier 2 method than to the Tier 1 method. Therefore, it is 

good practice to assess and document the quality of each activity data applied to the Tier 2 method and the 

completeness of the activity data prior to applying the Tier 2 method. If the data quality or completeness are 

deemed not adequate for application of the Tier 2 method then the Tier 1 method should be applied. 

Evaluation of Tier 3 method plant-specific data 

The Tier 3 method is based on the application of plant-specific emissions data. It is good practice for inventory 

compilers that conduct audits of plant-specific emissions estimates used in the inventory. This involves 

evaluating whether the plant-specific data are representative of plant emissions and, if plant-specific data for a 

specific plant are applied to the national inventory, evaluating whether the plant-specific data representative of 

petrochemical and carbon black production processes in the country as a whole. Audits of plant-specific data 

would involve the evaluation of: 

• Documentation of plant-specific measurement methodology; 

• Documentation of plant-specific measurement results; 

• Emissions estimation method and calculations; 

• Process feedstock(s) and product(s) 

• Activity data employed in emissions calculations; 

• Documentation of process technology and configuration; 

• List of assumptions; 

If the specific process for which plant-specific data are obtained is deemed not to be representative of other 

plants in the country producing the same petrochemical (e.g., if the feedstock differs or the process configuration 

differs) then the plant-specific data should not be applied to the overall inventory but only to the activity data for 

the specific plant. If emission measurements from individual plants are collected, inventory compilers should 

ensure that the measurements were made according to recognised national or international standards and the 

quality control methods were applied to the emissions measurement. Quality control procedures in use at the 

plant should be directly referenced and included in the quality control plan. If the measurement practices were 

not consistent with quality control standards or if the measurement procedures and results cannot be adequately 

documented, the inventory compiler should reconsider the use of the plant-specific data. 

3.9.4.2 REPORTING AND DOCUMENTATION

Combustion emissions from combustion of off gases generated by petrochemical production processes are 

attributed to the IPPU Sector source category which produces them, and are reported as industrial process 

emissions. However, if any portion of the off gases generated by an IPPU Sector source category is combusted 

within a different IPPU Sector source category, or combusted within an Energy Sector source category, the 

corresponding emissions are reported as fuel combustion emissions rather than as industrial process emissions. 

This means that if the combustion emissions occur within the IPPU Sector source category which produced the 

off gases, then the emissions are reported as industrial process emissions attributed to that IPPU Sector source 

category. However, if the off gases are transferred out of the process to another source category in the IPPU 

Sector or a source category in the Energy Sector, then the emissions from the combustion of the off gases are 

reported as fuel combustion emissions within that source category. When the total emissions from the 

combustion of the off gases are calculated, the quantity transferred to and reported in the Energy Sector and the 

quantity transferred to and reported in a different IPPU Sector source category should be clearly quantified in the 

IPPU Sector source category calculations and in the Energy Sector source category calculations. If a countryspecific emission factor was developed, the corresponding data should be provided as how the emission factor 

was developed and applied in the emission factor calculation, including reporting of the production process 

configuration upon which the emission factor and calculation are based. 

METHANOL 

The amount of methanol produced, the amount of natural gas feedstock consumed in methanol production, and 

the amount of supplemental CO2 feedstock consumed in methanol production are to be reported when available. 
Chapter 3: Chemical Industry Emissions 

2006 IPCC Guidelines for National Greenhouse Gas Inventories 3.89 

If a default emission factor is used, this should be noted in the reporting documentation, and the methanol 

production process configuration should be reported in the event that the default process configuration is not 

used. 

ETHYLENE 

The amount of each feedstock consumed in ethylene production and the amounts of ethylene and each other 

primary product produced and recovered as product are to be reported when available. If a default emission 

factor is used, this should be noted in the reporting documentation, and the ethylene production process 

configuration and feedstock(s) should be reported in the event that the default process configuration and default 

feedstock for the country/region are not used. 

ETHYLENE DICHLORIDE 

The amount of ethylene dichloride produced and ethylene feedstock consumed in ethylene dichloride production 

are to be reported when available. If a default emission factor is used, this should be noted in the reporting 

documentation, and the ethylene dichloride production process configuration should be reported in the event that 

the default process configuration is not used. 

ETHYLENE OXIDE 

The amount of ethylene oxide produced and ethylene feedstock consumed in ethylene oxide production are to be 

reported when available. If a default emission factor is used, this should be noted in the reporting documentation, 

and the ethylene oxide production process configuration should be reported in the event that the default process 

configuration is not used. 

ACRYLONITRILE 

The amount of propylene feedstock consumed in acrylonitrile production and the amounts of acrylonitrile, 

acetonitrile, and hydrogen cyanide produced and recovered as product are to be reported when available. If a 

default emission factor is used, this should be noted in the reporting documentation, and the acrylonitrile 

production process configuration should be reported in the event that the default process configuration is not 

used. 

CARBON BLACK 

The amount of carbon black produced and the amounts and characteristics (carbon content) of each primary and 

secondary feedstock consumed in carbon black production are to be reported when available. If a default 

emission factor is used, this should be noted in the reporting documentation, and the carbon black production 

process configuration should be reported in the event that the default process configuration is not used. 
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3. 90 2006 IPCC Guidelines for National Greenhouse Gas Inventories 

Annex 3.9A Feedstock-product flow diagrams 

Figure 3.11 Methanol production feedstock-product flow diagram 

Secondary Feedstock

Carbon Dioxide

Primary Feedstock

Natural Gas

Steam Reforming

Process

Methanol Product

Methanol

Production Process

Methanol Product

Purification

Vent Gas CO2 Flare CO2

Energy Recovery

Process

Vent Gas

Process

Purge Gas

Process Steam

Figure 3.12 Ethylene dichloride production feedstock-product flow diagram 

Primary Feedstock

Ethylene

Primary Feedstock

Ethylene

Vent Gas Incinerator

Oxychlorination

Process Reactor

Direct Chlorination

Process Reactor

Ethylene Dichloride

Purification Process

Ethylene Dichloride Product

Vent Gas CO2 Flare CO2

Chlorinated

Hydrocarbons

Process 

Vent Gas
Chapter 3: Chemical Industry Emissions 

2006 IPCC Guidelines for National Greenhouse Gas Inventories 3.91 

Figure 3.13 Ethylene oxide production feedstock-product flow diagram 

Primary Feedstock

Ethylene

Energy Recovery

Ethylene Oxide

Reactor Process

Ethylene Oxide

Product

Ethylene Oxide

Recovery Process

Flare CO2 Vent Gas CO2

Process 

Vent Gas

Figure 3.14 Acrylonitrile production feedstock-product flow diagram 

Primary Feedstock

Propylene

Energy Recovery

Ammoxidation

Reactor Process

Absorber

Vent Gas

Acrylonitrile Product

Purification

Product

Recovery Process

Flare CO2 Vent Gas CO2

No

Hydrogen Cyanide

By-product

Acetonitrile By-product

Acrylonitrile Product

Hydrogen

Cyanide

Recovery?

Acetonitrile

By-product

Recovery?

No

Yes

Yes

Figure 3.15 Carbon black production feedstock-product flow diagram 

Primary Feedstock

Carbon Black Feedstock

Energy Recovery

Furnace Black

Process Reactor

Carbon Black

Product Dryers

Flare CO2 Vent Gas CO2

Carbon Black

Product

Secondary Feedstock

Natural Gas

Process 

Vent Gas
Volume 3: Industrial Processes and Product Use 

3.92 2006 IPCC Guidelines for National Greenhouse Gas Inventories 

3.10 FLUOROCHEMICAL PRODUCTION 

3.10.1 HFC-23 emission from HCFC-22 production 

3.10.1.1 INTRODUCTION

Trifluoromethane (HFC-23 or CHF3), is generated as a by-product during the manufacture of 

chlorodifluoromethane (HCFC-22 or CHClF2).3

 Materials such as HFC-23 (and other HFCs, PFCs and SF6) are 

not significantly removed by aqueous (acidic, neutral or alkaline) scrubbing processes and will be released into 

the atmosphere. It is estimated that in 1990 the HFC-23 released from HCFC-22 plants was at most 4 percent of 

the production of HCFC-22 (U.S. EPA, 2001), in the absence of abatement measures. There are a small number 

of HCFC-22 production plants globally and thus a discrete number of point sources of HFC-23 emissions. While 

the methodology described here is applicable to by-product emissions of any fluorinated greenhouse gas, it has 

been written specifically for HFC-23. The methodology for emissions of fluorinated by-products in general and 

‘fugitive emissions’ is covered by Section 3.10.2. 

3.10.1.2 METHODOLOGICAL ISSUES

CHOICE OF METHOD 

There are two broad measurement approaches to estimating HFC-23 emissions from HCFC-22 plants. These are 

described in IPCC (2000), DEFRA (2002a and 2002b), EFCTC (2003) and UN (2004) and have been translated 

into Tier 2 and 3 methodologies described below. National emissions using either of these methodologies are the 

sum of those from the individual facilities. Tier 1 (default) methodology can be applied to individual plants or, if 

there is no abatement by destruction, to the total national output of HCFC-22. Accounting for HFC-23 emissions 

is not simply mechanistic but requires information on the process operations responsible for producing and 

emitting HFC-23, so that the most appropriate methodology and factors can be adopted. Therefore, it is good 

practice, to the extent possible, to establish contacts with plant managers in order to obtain the necessary data. 

The Tier 1 method is relatively simple, involving the application of a default emission factor to the quantity of 

HCFC-22 produced. This method can be applied at the plant level or the national level. Tier 2 and Tier 3 

methodologies are suitable only for plant level calculations because they rely on data that are only available from 

plants. In cases where there are Tier 3 data available for some plants, the Tier 1 or Tier 2 methods can be applied 

to the remainder to ensure complete coverage. 

It is good practice to estimate national emissions by summing measured parameters from all HCFC-22 plants in 

a country. Tier 3 plant emission measurements are the most accurate, followed by Tier 2 measurements based on 

plant efficiencies. Direct measurement is significantly more accurate than Tier 1 because it reflects the 

conditions specific to each manufacturing facility. In most cases, the data necessary to prepare Tier 3 estimates 

should be available because facilities operating to good business practice perform regular or periodic sampling of 

the final process vent or within the process itself as part of routine operations. The Tier 1 (default) method 

should be used only in cases where plant-specific data are unavailable and this subcategory is not identified as 

significant subcategory under key category. (See Section 4.2 of Volume 1.) Modern plant using process 

optimization will need to keep accurate HFC-23 generation data as part of this optimization, so plant-specific 

data should be available to most countries in most cases. 

The choice of good practice method will depend on national circumstances. The decision tree in Figure 3.16 

describes good practice in adapting the methods in these Guidelines to country-specific circumstances. 

Procedures to abate emissions include destruction of HFC-23 in a discrete facility and, in this case, emissions 

occur only when the destruction facility is not in operation. The tiers of methodology provide estimates for the 

quantity of HFC-23 that is produced and the share of production that is ultimately emitted depends on the length 

of time that the destruction facility is not operated. For facilities using abatement techniques such as HFC-23 

destruction, verification of the abatement efficiency is also done routinely. It is good practice to subtract abated 

HFC-23 emissions from national estimates where the abatement has been verified by process records on every 

plant. 

 

3

 HCFC-22 is used as a refrigerant in several different applications, as a blend component in foam blowing, and as a 

chemical feedstock for manufacturing synthetic polymers. 
Chapter 3: Chemical Industry Emissions 

2006 IPCC Guidelines for National Greenhouse Gas Inventories 3.93 

Tier 1 

In the Tier 1 methodology, a default factor is used to estimate production (and potential emissions) of HFC-23 

from the total HCFC-22 production from each facility (for both potentially dispersive uses, as reported under the 

Montreal Protocol, and feedstock uses, which are reported separately to the Ozone Secretariat). See Equation 

3.30. 

EQUATION 3.30 

TIER 1 CALCULATION OF HFC-23 FROM HCFC-22 (PRODUCED) USING DEFAULT FACTOR

−23 −22 EHFC = EFdefault • PHCFC

Where: 

EHFC-23 = by-product HFC-23 emissions from HCFC-22 production, kg 

EFdefault = HFC-23 default emission factor, kg HFC-23/kg HCFC-22 

PHCFC-22 = total HCFC-22 production, kg 

This methodology is suitable where plant-specific measurements are not available and, in that case, the default 

condition is that all of the estimated HFC-23 production is released into the atmosphere. 

Tier 2 

In the Tier 2 methodology, the HFC-23 emission factor is derived from records of process efficiencies and used 

in the calculation shown as Equation 3.31. This is a material balance approach and relies on calculating the 

difference between the expected production of HCFC-22 and the actual production and then assigning that 

difference to loss of raw materials, loss of product (HCFC-22) and conversion to by-products, including HFC-23. 

These parameters will be different for each plant and so should be assessed separately for each facility reporting 

into the national data. 

EQUATION 3.31 

TIER 2 CALCULATION OF HFC-23 FROM HCFC-22 (PRODUCED) USING FACTOR(S) CALCULATED 

FROM PROCESS EFFICIENCIES

EHFC EFcalculated PHCFC Freleased = • • −23 −22

Where: 

EHFC-23 = by-product HFC-23 emissions from HCFC-22 production, kg 

EFdefault = HFC-23 calculated emission factor, kg HFC-23/kg HCFC-22 

PHCFC-22 = total HCFC-22 production, kg 

Freleased = Fraction of the year that this stream was released to atmosphere untreated, fraction 

The emission factor can be calculated from both the carbon efficiency (Equation 3.32) and the fluorine efficiency 

(Equation 3.33) and the value used in Equation 3.31 should normally be the average of these two values unless 

there are overriding considerations (such as a much lower uncertainty of one of the efficiency measures) that can 

be adequately documented. Annual average carbon and fluorine balance efficiencies are features of a wellmanaged HCFC-22 plant and are either normally available to the plant operator or may be obtained by 

examination of process accounting records. Similarly, if there is a vent treatment system, the length of time that 

this was in operation, and treating the vent stream from the HCFC-22 plant, should be available from records.

Total HCFC-22 production includes material that is used as a chemical feedstock as well as that which is sold for 

potentially dispersive uses.

EQUATION 3.32 

CALCULATION OF HFC-23 EMISSION FACTOR FROM CARBON BALANCE EFFICIENCY

( ) F FCC CBE EFcarbon balance efficiency loss • • − = 100

100 _

Where: 

EFcarbon_balance = HFC-23 emission factor calculated from carbon balance efficiency, kg HFC-23/kg HCFC-22 

CBE = carbon balance efficiency, percent 
Volume 3: Industrial Processes and Product Use 

3.94 2006 IPCC Guidelines for National Greenhouse Gas Inventories 

Fefficiency loss = factor to assign efficiency loss to HFC-23, fraction 

FCC = factor for the carbon content of this component (= 0.81), kg HFC-23/kg HCFC-22 

and 

EQUATION 3.33 

CALCULATION OF HFC-23 EMISSION FACTOR FROM FLUORINE BALANCE EFFICIENCY

( ) F FFC FBE EFfluorine balance efficiency loss • • − = 100

100 _

Where: 

EFfluorine_balance = HFC-23 emission factor calculated from fluorine balance efficiency, kg HFC-23/kg 

HCFC-22 

FBE = fluorine balance efficiency, percent 

Fefficiency loss = factor to assign efficiency loss to HFC-23, fraction 

FFC = factor for the fluorine content of this component (= 0.54), kg HFC-23/kg HCFC-22 

The factor to assign the efficiency loss to HFC-23 is specific to each plant and, if this method of calculation is 

used, the factor should have been established by the process operator. By default, the value is 1; that is all of the 

loss in efficiency is due to co-production of HFC-23. In practice, this is commonly the most significant 

efficiency loss, being much larger than losses of raw materials or products. 

The factors for carbon and fluorine contents are calculated from the molecular compositions of HFC-23 and 

HCFC-22 and are common to all HCFC-22 plants at 0.81 for carbon and 0.54 for fluorine. 

Tier 3 

Tier 3 methodologies are potentially the most accurate. The Tier 3 methodologies provided here give equivalent 

results and the choice between them will be dictated by the information available in individual facilities. In each 

case, the national emission is the sum of factory specific emissions, each of which may be determined using a 

Tier 3 method to estimate the composition and flowrate of gas streams vented to atmosphere (either directly and 

continuously – as in Tier 3a - or by continuous monitoring of a process parameter related to the emission - Tier 

3b - or by monitoring the HFC-23 concentration continuously within the reactor product stream - Tier 3c): 

EQUATION 3.34 

TIER 3a CALCULATION OF HFC-23 EMISSIONS FROM INDIVIDUAL PROCESS STREAMS

(DIRECT METHOD) 

∑ ∑ ∫ = • − i j t HFC ij ij E C f 23 [ ∫t means the quantity should be summed over time.]

Where: 

EHFC-23 = total HFC-23 emissions: the sum over all i plants, over all j streams in each plant of the emitted 

mass flows f and concentrations C is integrated over time t. (See Equation 3.37 for calculation of 

‘instantaneous’ HFC-23 emissions in an individual process stream.) 

or, where proxy methodology is used: 

EQUATION 3.35 

TIER 3b CALCULATION OF HFC-23 EMISSIONS FROM INDIVIDUAL PROCESS STREAMS

(PROXY METHOD) 

− = ∑ ∑ ∫

i j t EHFC 23 Eij [ ∫t means the quantity should be summed over time.] 

Where: 

EHFC-23 = total HFC-23 emissions: Ei,j are the emissions from each plant and stream determined by the 

proxy methods. (See Equation 3.38 for calculation of HFC-23 emissions in an individual process 

stream.) 

or, where the HFC-23 concentration within the reactor product stream is used: 
Chapter 3: Chemical Industry Emissions 

2006 IPCC Guidelines for National Greenhouse Gas Inventories 3.95 

EQUATION 3.36 

TIER 3c CALCULATION OF HFC-23 EMISSIONS FROM INDIVIDUAL PROCESS STREAMS

(BY MONITORING REACTOR PRODUCT) 

∑ ∫ = • − i t EHFC 23 Ci Pi [ ∫t means the quantity should be summed over time.] 

Where:

EHFC-23 = total HFC-23 emissions: Pi is the mass flow of HCFC-22 product from the plant reactor at the 

plant i, and Ci is the concentration of HFC-23 relative to the HCFC-22 product at the plant i. (See 

Equation 3.40 for calculation of HFC-23 emissions at an individual facility by in-process 

measurement.) 

Tier 3a 

The Tier 3a method is based on frequent or continuous measurement of the concentration and flow-rate from the 

vent at an individual plant. So that the quantity emitted to atmosphere is the mathematical product of the mass 

concentration of the component in the stream, the flowrate of the total stream (in units compatible with the mass 

concentration) and the length of time that this flow occurred: 

EQUATION 3.37 

TIER 3a CALCULATION OF ‘INSTANTANEOUS’ HFC-23 EMISSIONS IN AN INDIVIDUAL PROCESS 

STREAM (DIRECT METHOD) 

E C f t ij ij ij = • •

Where: 

Eij = ‘instantaneous’ HFC-23 emissions from process stream j at plant i, kg 

Cij = the concentration of HFC-23 in the gas stream actually vented from process stream j at plant i, 

kg HFC-23/kg gas 

fij = the mass flow of the gas stream from process stream j at plant i (generally measured volumetrically 

and converted into mass flow using standard process engineering methods), kg gas/hour 

t = the length of time over which these parameters are measured and remain constant, hours 

If any HFC-23 is recovered from the vent stream for use as chemical feedstock, and hence destroyed, it should 

be discounted from this emission; material recovered for uses where it may be emitted may be discounted here, if 

the emissions are included in the quantity calculated by the methods in Chapter 7. Because emissions are 

measured directly in this tier, it is not necessary to have a separate term for material recovered, unlike Tiers 3b 

and 3c.

The total quantity of HFC-23 released is then the annual sum of these measured instantaneous releases. Periods 

when the vent stream is processed in a destruction unit to remove HFC-23 should not be counted in this 

calculation. If it is necessary to estimate the quantity destroyed at each facility, the operator should calculate this 

based on the difference between the operating time of the plant and the duration of release (t above).

Tier 3b 

In many cases, measurements are not continuous but were gained during an intensive process survey or plant 

trial, and the results of the trial may be used to provide a proxy for calculating emissions during normal plant 

operation. In this case, the emission rate of the by-product is related to a more easily (or accurately) measurable 

parameter, such as feedstock flow rate. The trial(s) must meet the following conditions: 

• There should have been no major process design, construction or operating changes that affect the plant 

upstream of the measurement point and so could render relationships between emissions and production 

invalid. (See also Box 3.14) 

• The relationship between emissions and plant operating rate must be established during the trial(s), together 

with its uncertainty. 

For almost all cases the rate of plant operation is a suitable proxy and the quantity of HFC-23 emitted depends 

on the current plant operating rate and the length of time that the vent flow was released. 
Volume 3: Industrial Processes and Product Use 

3.96 2006 IPCC Guidelines for National Greenhouse Gas Inventories 

EQUATION 3.38 

TIER 3b CALCULATION OF HFC-23 EMISSIONS IN AN INDIVIDUAL PROCESS STREAM

(PROXY METHOD) 

ij ij ij ij Rij E = S • F • POR •t −

Where: 

Eij = the mass emission of HFC-23 in vent stream j at plant i, kg 

Sij = the standard mass emission of HFC-23 in vent stream j at plant i per ‘unit’ of proxy quantity, such as 

process operating rate (described in Equation 3.39, below), kg/‘unit’ 

Fij = a dimensionless factor relating the measured standard mass emission rate to the emission rate at the 

actual plant operating rate. In many cases, the fraction produced is not sensitive to operating rate and 

Fi is unity (i.e., the emission rate is proportional to operating rate). In other cases the emission rate is 

a more complex function of the operating rate. In all cases Fi should be derived during the plant trial 

by measuring HFC-23 production at different operating rates. For situations where a simple function 

relating the emissions to the operating rate cannot be determined from testing, the proxy method is 

not considered appropriate and continuous measurement is desirable. 

PORij = the current process operating rate applicable to vent stream j at plant i averaged over t in 

‘unit/hour’. The units of this parameter must be consistent between the plant trial establishing the 

standard emission rate and the estimate of ongoing, operational emissions (described in Equation 

3.39, below). 

t = the actual total duration of venting for the year, or the period if the process is not operated 

continuously in hours. Annual emissions become the sum of all the periods during the year. The 

periods during which the vent stream is processed in a destruction system should not be counted here. 

Rij = the quantity of HFC-23 recovered for vent stream j at plant i for use as chemical feedstock, and 

hence destroyed, kg. Material recovered for uses where it may be emitted potentially may be counted 

here if the emissions are included in the quantity calculated by the methods for ODS substitutes in 

Chapter 7 of this volume.

EQUATION 3.39 

TIER 3b CALCULATION OF STANDARD EMISSION FOR PROXY METHOD

T ij T ij T ij PORT ij S C f , , , , = •

Where (for each test T): 

Sij = the standard mass emission of HFC-23 in vent stream j at plant i, kg/‘unit’ (in units compatible with 

the factors in Equation 3.38, see PORT,ij below) 

CT,ij = the average mass fractional concentration of HFC-23 in vent stream j at plant i during the trial, 

kg/kg 

f T,ij= the average mass flowrate of vent stream j at plant i during the trial, kg/hour 

PORT,ij = the proxy quantity (such as process operating rate) at plant i during the trial, ‘unit’/hour. The 

‘unit’ depends on the proxy quantity adopted for plant i vent stream j (for example, kg/hour or 

m3

/hour of feedstock) 

Tier 3c 

It is a relatively simple procedure to monitor the concentration of HFC-23 in the product of a reaction system 

relative to the amount of HCFC-22. This provides a basis for estimation of the quantity of HFC-23 released as 

the mathematical product of the monitored concentration and the mass flow of HCFC-22 made. If there is no 

vent treatment to abate emissions, this is a simple procedure. However, where there is abatement then it must be 

shown that this actually treats all streams that may be released into the atmosphere, including direct gas vents 

and the outgassing of aqueous streams. The latter, especially, may not be passed to the destruction facility. If all 

potential vent streams are not treated, the method cannot be used. 
Chapter 3: Chemical Industry Emissions 

2006 IPCC Guidelines for National Greenhouse Gas Inventories 3.97 

EQUATION 3.40 

TIER 3c CALCULATION OF HFC-23 EMISSIONS FROM AN INDIVIDUAL FACILITY BY IN-PROCESS 

MEASUREMENT

i i j F Ri E = C • P •t −

Where: 

Ei = HFC-23 emissions from an individual facility i, kg 

Ci = the concentration of HFC-23 in the reactor product at facility i, kg HFC-23/kg HCFC-22 

Pi = the mass of HCFC-22 produced at facility i while this concentration applied, kg 

tF = the fractional duration during which this HFC-23 is actually vented to the atmosphere, rather than 

destroyed, fraction 

Ri = the quantity of HFC-23 recovered from facility i for use as chemical feedstock, and hence destroyed, 

kg 

Material recovered for uses where it may be emitted potentially may be counted here if the emissions 

are included in the quantity calculated by the methods in Chapter 7 of this volume. 

The total quantity of HFC-23 released into the atmosphere is the sum of the quantities from the individual 

release periods and individual reaction systems. 

HFC-23 that is recovered for use as chemical feedstock should be subtracted from the total quantity estimated 

here. 

In summary, the Tier 1 method is relatively simple, involving the application of a default emission factor to the 

quantity of HCFC-22 produced. This method can be applied at the plant level or the national level. Tier 2 and 

Tier 3 methodologies are suitable only for plant level calculations. In cases where there are Tier 3 data available 

for some plants, the Tier 1 or Tier 2 methods can be applied to the remainder to ensure complete coverage. 

Uncertainty in the national emission is then calculated using production weighted uncertainties of the individual 

sources and standard statistical techniques. Regardless of the method, emissions abated should be subtracted 

from the gross estimate from each plant to determine net emissions before these are added together in the 

national estimate. 
Volume 3: Industrial Processes and Product Use 

3.98 2006 IPCC Guidelines for National Greenhouse Gas Inventories 

Figure 3.16 Decision tree for HFC-23 emissions from HCFC-22 production (or other 

similar by-product emissions from fluorochemical production) 

Start

Are

plant-level

HFC-23 measurement

data available?

Is the

Fluorochemical

Production a key category1

, 

and is this subcategory

significant?

No

No

Obtain plant-level HFC23 measurement data.

Estimate emissions by 

aggregating plant-level

measurements, and

estimates for plants

without measurements2

,

adjusting for HFC-23

destruction.

Aggregate plant-level

emissions.

Box 2: Tier 2

Box 5: Tier 3

Note:

1. See Volume 1 Chapter 4, Methodological Choice and Identification of Key Categories (noting Section 4.1.2 on limited resources), for 

discussion of key categories and use of decision trees.

2. If there are Tier 3 data available for some plants, the Tier 1 or Tier 2 methods can be applied to the remainder to ensure complete 

coverage.

Yes

Yes

Are

plant-level

HCFC-22 production

data

available?

Aggregate plant-level 

emissions, adjusting for

HFC-23 destruction.

Box 3: Tier 2

Yes

Yes

Does any

HFC-23 destruction

take place?

Calculate plantlevel emissions

using the Tier 2 

emission factor.

Collect national

HCFC-22

production data.

Calculate plant-level 

emissions using

plant-level data and

Tier 3a, 3b or 3c 

methodology.

Yes

No

Estimate emissions using the default No

emission factor. If the emissions are 

estimated at the plant level, aggregate 

plant-level emissions.

Estimate emissions by 

aggregating plant-level

measurements2

, and

estimates for plants

without measurements.

Are

plant-level

efficiencies

available?

Is it

possible to

document any

HFC-23

destruction?

No

Yes

Box 1: Tier 1

Box 4: Tier 3

No

It is good practice to use the Tier 3 method if possible. Direct measurement is significantly more accurate than 

Tier 1 because it reflects the conditions specific to each manufacturing facility. In most cases, the data necessary 

to prepare Tier 3 estimates should be available because facilities operating to good business practice perform 

regular or periodic sampling of the final process vent or within the process itself as part of routine operations. 

For facilities using abatement techniques such as HFC-23 destruction, verification of the abatement efficiency is 

also done routinely. The Tier 1 (default) method should be used only in rare cases where plant-specific data are 

unavailable and this subcategory is not identified as significant subcategory under key category. (See Section 4.2 

of Volume 1.) 
Chapter 3: Chemical Industry Emissions 

2006 IPCC Guidelines for National Greenhouse Gas Inventories 3.99 

CHOICE OF EMISSION FACTORS 

There are several measurement options within the Tier 3 method relating to the location and frequency of the 

sampling. In general, direct measurement of the emissions of HFC-23 may provide the highest accuracy but 

continuous or frequent measurement of parameters within the production process area itself may be more 

pragmatic and can be equally accurate. In both cases, the frequency of measurement must be high enough to 

represent the variability in the process (e.g., across the life of the catalyst). Issues related to measurement 

frequency are summarised in Box 3.14, Plant Measurement Frequency. General advice on sampling and 

representativeness is provided in Volume 1, Chapter 2. 

In cases where plant-specific measurements or sampling are not available and Tier 1 methods are used, the 

default emission factor should be used, assuming no abatement methods. For plants in operation prior to 1995

the default emission factor is 0.04 kg HFC-23/kg HCFC-22 (4 percent) (IPCC, 1996; USEPA, 2001). This is a 

default to be used when there are no measurements and describes the output of HFC-23 from a typical HCFC-22 

plant in the absence of recovery or destruction of HFC-23. The value is consistent with atmospheric observations 

of HFC-23 concentrations in the 1978-1995 time period (Oram et al.,1998). These showed globally averaged 

emissions to be equivalent to 2 percent of the total quantity of HCFC-22 produced at a time when significant 

HFC-23 was being recovered and converted into Halon 1301 (McCulloch, 1992) and abatement was required 

practice in several countries where there was significant production. 

It is possible, by process optimisation, to reduce the production to between 0.014 and 0.03 kg HFC-23/kg 

HCFC-22 (1.4 to 3 percent) but it is not possible to completely eliminate HFC-23 formation this way (IPCC, 

2000). Furthermore, the extent of the reduction is highly dependent on the process design and the economic 

environment (measures to reduce HFC-23 can often reduce the process output). In an optimised process HFC-23 

production and emissions will, invariably, have been measured; it is not possible to optimise process operation 

without such measurements and so default values have no meaning in this context for an individual plant. 

However, the state of the technological art has been advanced by optimisation of individual plants and that art 

should have been built into the design of recent plants, suggesting a default emission factor of 0.03 kg HFC23/kg HCFC-22 (3 percent). These default values have a large uncertainty (in the region of 50 percent). For more 

accurate assessments, the actual emissions should be determined by Tier 2 or Tier 3 methodology and, if 

necessary, assigned to previous years using the guidance provided in Chapter 7 of this volume. 

TABLE 3.28 

HFC-23 DEFAULT EMISSION FACTORS

Technology Emission Factor 

(kg HFC-23/kg HCFC-22 produced) 

Old, unoptimised plants (e.g., 1940s to 1990/1995) 0.04 

Plants of recent design, not specifically optimised 0.03 

Global average emissions (1978 - 1995)4 0.02 

For comparison: 

Optimised large plant- requiring measurement of HFC-23 (Tier 3) 

Plant with effective capture and destruction of HFC-23 (Tier 3) 

Down to 0.014 

Down to zero

 

4

 The global average is calculated from the change in atmospheric concentration of HFC-23. It does not discriminate 

between plant emissions, which range from nothing to greater than 4 percent of the HCFC-22 production. 
Volume 3: Industrial Processes and Product Use 

3.100 2006 IPCC Guidelines for National Greenhouse Gas Inventories 

BOX 3.14 

PLANT MEASUREMENT FREQUENCY

The accuracy and precision of the estimates of annual HFC-23 emissions depend on the number of 

samples (the frequency of sample collection) together with the accuracy of measurement of 

flowrates and the extent to which discrete flow measurements can represent the total quantity 

vented. Since production processes are not completely static, the greater the process variability, the 

more frequently plants need to measure. As a general rule, sampling and analysis should be 

repeated whenever a plant makes any significant process changes. Before choosing a sampling 

frequency, the plant should set a goal for accuracy and use statistical tools to determine the sample 

size necessary to achieve the goal. For example, a study of HCFC-22 producers indicates that 

sampling once per day is sufficient to achieve an extremely accurate annual estimate. This 

accuracy goal should then be revised, if necessary, to take into account the available resources. 

(RTI, Cadmus, 1998)

CHOICE OF ACTIVITY DATA 

When using the Tier 1 method, production data should be obtained directly from producers. There are several 

ways producers may determine their production levels, including shipment weights and measuring volumetimes-density, using flow meters. These data should account for all HCFC-22 production for the year, whether 

for sale or for use internally as feedstock, and the plant should describe how the HCFC-22 production rate is 

determined. In some circumstances, producers may consider plant production data to be confidential. For 

national-level activity data, submission of HCFC-22 production data is already required under the Montreal 

Protocol. 

COMPLETENESS 

It should be possible to obtain complete sampling data because there are only a small number of HCFC-22 plants 

in each country, and it is standard practice for each plant operator to monitor process efficiencies and hence 

HFC-23 losses, leading to the adoption of Tier 2 methodology. The destruction efficiencies of thermal oxidisers 

used to abate HFC-23 are generally high (>99 percent) but it is important to establish the composition of the exit 

gas in order to ensure that account is taken of emissions of fluorinated greenhouse gases from this point. 

DEVELOPING A CONSISTENT TIME SERIES 

Emission of HFC-23 from HCFC-22 production should be estimated using the same method for the entire time 

series and appropriate emission factors. If data for any years in the time series are unavailable for the Tier 3 

method, these gaps should be filled according to the guidance provided in Volume 1, Chapter 5. 

3.10.1.3 UNCERTAINTY ASSESSMENT

TIER 1 

Unlike the other Tiers, where uncertainties are based on measurements and statistics, Tier 1 uncertainties are 

assessed through expert judgement and an error of approximately 50 percent could be considered for Tier 1 

based upon knowledge of the variability in emissions from different manufacturing facilities. An error of this 

magnitude will completely outweigh the uncertainty in the activity. 

TIER 2 

Uncertainty of the Tier 2 result is calculated by the root-squared sum of the individual uncertainties in 

production mass quantity and efficiencies, assuming the carbon and fluorine uncertainties are the same. Where 

the uncertainties in carbon and fluorine efficiency differ significantly (enough to cause a material difference to 

the calculated emission), the value with the lower uncertainty should be used throughout the calculation. 

Uncertainty in the value derived by Tier 2 methods is much larger than that expected from Tier 3 but is, 

nevertheless, quantifiable. Typically, for a plant producing about 4 percent HFC-23, the carbon efficiency is in 

the region of 95 percent and the fluorine efficiency 92 percent. If these efficiencies can be measured to within 1 

percent, then the error in the Tier 2 HFC-23 estimate would be less than 20 percent. Estimating efficiencies to 

this degree of accuracy will require rigorous accounting procedures and that all raw materials and product for 

sale should be weighed in or out of the facility. Such a regime sets the expected accuracy of the overall activity 

(for both Tiers 1 and 2); with good accounting and measurement of production by weight, it should be possible 

to reduce the error in the activity to below 1 percent. 
Chapter 3: Chemical Industry Emissions 

2006 IPCC Guidelines for National Greenhouse Gas Inventories 3.101 

TIER 3 

For HFC-23, the Tier 3 method is significantly more accurate than either the Tier 2 measured or Tier 1 default 

methods. Regular Tier 3 sampling of the vent stream can achieve an accuracy of 1-2 percent at a 95 percent 

confidence level in HFC-23 emissions and the uncertainty of the Tier 3 (proxy) result may be similar. In both 

cases, the uncertainty may be calculated statistically from the uncertainties of the input parameters and, because 

these methods do not rely on emission factors or activities, the concept of subdividing uncertainty has no validity. 

Uncertainty of the estimate is expressed as a coefficient of variance (percent) and, for each of these streams, 

there will be an uncertainty as a consequence of uncertainties in measured concentration and flowrate and 

uncertainty in the duration of the flow. The combined uncertainty can be determined analytically and should be 

calculated using the standard methodology described in Chapter 3 of Volume 1.

3.10.1.4 QUALITY ASSURANCE/QUALITY CONTROL (QA/QC),

REPORTING AND DOCUMENTATION

QUALITY ASSURANCE/QUALITY CONTROL 

It is good practice to conduct quality control checks as outlined in Volume 1, Chapter 6, and an expert review of 

the emissions estimates. Additional quality control checks as outlined in Volume 1, Chapter 6, and quality 

assurance procedures may also be applicable, particularly if higher tier methods are used to determine emissions 

from this source category. Inventory compilers are encouraged to use higher tier QA/QC for key categories as 

identified in Volume 1, Chapter 4. 

In addition to the guidance in Volume 1, specific procedures of relevance to this sub-source category are 

outlined below: 

Comparison of emissions estimates using different approaches 

Inventory compilers should compare reported plant emissions estimates against those determined using the Tier 

1 default factor and production data. If only national production data are available, they should compare 

aggregated plant emissions to a national default estimate. If significant differences are found in the comparison, 

they should answer the following questions: 

1. Are there inaccuracies associated with any of the individual plant estimates (e.g., an extreme outlier may be 

accounting for an unreasonable quantity of emissions)? 

2. Are the plant-specific emission factors significantly different from one another? 

3. Are the plant-specific production rates consistent with published national level production rates? 

4. Is there any other explanation for a significant difference, such as the effect of controls, the manner in which 

production is reported or possibly undocumented assumptions? 

Direct emission measurement check 

• Inventory compilers should confirm that internationally recognised, standard methods were used for plant 

measurements. If the measurement practices fail this criterion, then the use of these emissions data should be 

carefully evaluated. It is also possible that, where a high standard of measurement and QA/QC is in place at 

sites, the uncertainty of the emissions estimates may be revised downwards. 

• Each plant’s QA/QC process should be evaluated to assess if the number of samples and the frequency of 

sample collection is appropriate given the variability in the process itself. 

• Where possible, inventory compilers should verify all measured and calculated data through comparison 

with other systems of measurement or calculation. For example, emissions measurement within the process 

itself can be verified periodically with measurement of the vent stream. Inventory compilers should verify 

abatement system utilisation and efficiency. 

• With a periodic external audit of the plant measurement techniques and results, it is also possible to compare 

implied emission factors across plants and account for major differences. 

REPORTING AND DOCUMENTATION 

It is good practice to document and archive all information required to produce the national emissions inventory 

estimates as outlined in Volume 1, Section 6.11. 

Some examples of specific documentation and reporting relevant to this source category are provided below: 
Volume 3: Industrial Processes and Product Use 

3.102 2006 IPCC Guidelines for National Greenhouse Gas Inventories 

• To provide for completely transparent reporting, emissions of HFC-23 from HCFC-22 production should be 

reported as a separate item, rather than included with other HFC emissions. 

• Documentation should also include: 

(i) Methodological description; 

(ii) Number of HCFC-22 plants; 

(iii) HCFC-22 production (if multiple producers); 

(iv) Presence of abatement technology; 

(v) Process descriptions, operating parameters; and 

(vi) Related emission factors. 

Confidentiality 

• The use of the Tiers 2 and 3 methods would mean that the plant emissions of HFC-23 are reported 

separately from the production of HCFC-22. By de-coupling the HFC-23 emissions and HCFC-22 

production, the emission data on HFC-23 cannot be considered to be of commercial confidence as it does 

not reveal the levels of production of HCFC-22 without detailed and confidential knowledge of the 

individual manufacturing facility.

• The application of the Tier 1 method to total national production of HCFC-22 would enable this to be 

calculated from published emissions of HFC-23 and, if there were less than three producers, such production 

data could be considered confidential business information. In such cases, steps should be taken to protect 

confidentiality through, for example, the aggregation of all HFC emissions. For transparency reasons, 

whenever there is aggregation, a qualitative discussion of HCFC-22 production should be included. 

• When national emissions are calculated as the sum from individual facilities and these have been calculated 

using different methodologies, it is not possible to recalculate the HCFC-22 production from these data 

alone and there should be no problems concerning confidentiality. 

3.10.2 Emissions from production of other fluorinated 

compounds 

3.10.2.1 INTRODUCTION

A large number of fluorine containing greenhouse gases can be produced as by-products of fluorochemical 

manufacture and emitted into the atmosphere. For example, in a recent national inventory, significant by-product 

emissions of SF6, CF4, C2F6, C3F8, C4F10, C5F12 and C6F14 were reported for a fluorochemical plant (UNFCCC, 

2005). Other examples include the release of by-product CF4 from the production of CFC-11 and 12 or of SF6

from the production of uranium hexafluoride in the nuclear fuel cycle. 

Emissions of a chemical occur during its production and distribution or as a by-product during the production of 

a related chemical (HFC-23 from HCFC-22 production is covered specifically in Section 3.10.1 above). There 

may also be emissions of the material that is being produced; the so-called ‘fugitive emissions’. Both by-product 

and fugitive emissions are calculated in the same way. In this section, emissions associated with use are not 

addressed specifically, being counted in the emissions related to consumption (see Chapters 4.5, 6, 7 and 8 in 

this volume). Typically, fluorochemicals may be released from chemical processes involving a broad range of 

technologies and processes5

: 

• Telomerization Process used in the production of fluorochemicals fluids and polymers 

• Photooxidation of tetrafluoroethylene to make fluorochemical fluids 

• Direct Fluorination often used in SF6 production 

• Halogen Exchange Processes to make low boiling PFCs like C2F6 and CF4, HFC 134a and 245fa 

• NF3 manufacturing by direct fluorination 

• Production of uranium hexafluoride 

 

5

 This list is illustrative. 
Chapter 3: Chemical Industry Emissions 

2006 IPCC Guidelines for National Greenhouse Gas Inventories 3.103 

• Production of fluorinated monomers like tetrafluoroethylene and hexafluoropropylene 

• Production of fluorochemical agrochemcials 

• Production of fluorochemical anesthetics 

Halogen exchange processes are extensively used for HFC manufacture, while most PFCs and SF6 require 

elemental fluorine, generated electrochemically. In ‘electrochemical fluorination’ processes, the fluorine is not 

separated but makes the desired product in the electrochemical cell. In other processes it is separated and 

subsequently used, either as the elemental gas or as a component of a carrier system, such as CoF3. Each process 

will have a different spectrum of emissions, in terms of both chemical nature and quantities, and so a common 

default emission function is of relatively little value. It is essential that the existence of potentially emissive 

plants is identified within each country, hence this step is first in the decision tree (Figure 3.17). The common 

factor for these plants is the use of anhydrous hydrogen fluoride, which is the source of fluorine in halogen 

exchange processes and in processes that use elemental fluorine. The production and importation of anhydrous 

hydrogen fluoride can therefore be used as a means of tracing significant producers of fluorochemicals. Further 

enquiries (see Figure 3.17) can then elucidate whether or not there are significant fluorochemical greenhouse gas 

emissions. 

3.10.2.2 METHODOLOGICAL ISSUES

CHOICE OF METHOD 

It is good practice to choose the method using the decision tree shown in Figure 3.17. If the Category 2B9 

Fluorochemical Production is identified as key and this subcategory is judged to be significant, inventory 

compilers should consider whether or not emissions are dominated by the production of a sub-set of chemicals, 

and focus more sophisticated data collection efforts on production of these chemicals. The number of major 

producers of these fluorinated greenhouse gases is quite small: in the case of SF6, there are globally about 6 

companies with about 10 production facilities world-wide (Preisegger, 1999). The number of smaller producers 

may grow in the near future, particularly in developing economies. However, a survey of national producers 

should not be difficult to compile. 

Tier 1 

In the Tier 1 methodology, a default emission factor, or a similar number derived for the particular country's 

circumstances, can be used to estimate national production-related emissions of individual HFCs, PFCs, SF6 and 

other fluorinated greenhouse gases. 

EQUATION 3.41 

TIER 1 CALCULATION OF PRODUCTION-RELATED EMISSIONS

Ek EFdefault k Pk = • ,

Where: 

Ek = production-related emissions of fluorinated greenhouse gas k, kg 

EFdefault, k = default emission factor, kg/kg 

Pk = total production of fluorinated greenhouse gas k, kg 

Problems of confidentiality arising from reporting specific component data can be circumvented by providing a 

single number for total national emissions of each HFC, PFC and SF6. This may be facilitated if data are 

collected by a third party and reported only as this total. 

Tier 2 

The method based on process efficiencies, which works for HFC-23 emissions from HCFC-22 plants, is of less 

value for other types of plants. This is due in part to the lower inefficiency expected from these other by-product 

emissions; the uncertainty in measurement of efficiencies is likely to be much greater than the by-product 

emission factor. Furthermore, a range of by-products may be responsible for process inefficiency (unlike the case 

for HCFC-22 where one by-product predominates). However, production efficiency data should exist for each 

process and, in the absence of a more rigorous estimate, the quantity of emissions estimated from process 

inefficiencies may be used in a qualitative decision as to whether or not these emissions are a significant 

subcategory under a key category (in which case, Tier 3 methodology is specified). 
Volume 3: Industrial Processes and Product Use 

3.104 2006 IPCC Guidelines for National Greenhouse Gas Inventories 

Tier 3 

The Tier 3 methodology is potentially the most accurate estimate and is the sum of factory specific emissions of 

each by-product fluorinated greenhouse gas determined using standard methods to estimate the composition and 

flowrate of gas streams actually vented to atmosphere after any abatement technology. In this case: 

EQUATION 3.42 

TIER 3 DIRECT CALCULATION OF PRODUCTION-RELATED EMISSIONS

∑ ∑ ∫ = • i j t k ijk ijk E C f [ ∫t means the quantity should be summed over time.]

Where: 

Ek = total production-related emissions of fluorinated greenhouse gas k: the sum over all i plants, over all 

j streams in each plant of the emitted mass flows f and concentrations C integrated over time t. 

or, where proxy methodology is used, for example where the emission rate of the by-product is normalised to a 

more easily (or accurately) measurable parameter, such as feedstock flow rate, as described in Equation 3.35 in 

Section 3.10.1: 

EQUATION 3.43 

TIER 3 PROXY CALCULATION OF PRODUCTION-RELATED EMISSIONS

= ∑ ∑ ∫

i j t Ek Eijk [ ∫t means the quantity should be summed over time.] 

Where: 

Ek = total production-related emissions of fluorinated greenhouse gas k: Eijk = the emissions of 

fluorinated greenhouse gas k from each plant and stream determined by the proxy methods, described 

in Equations 3.38 and 3.39 in Section 3.10.1 

Note that, generally, flows are measured volumetrically and should be converted into mass flow (kg/hour) based 

on the ideal gas law, temperature, pressure and composition, similarly concentration should be converted into 

compatible units (e.g., kg/kg). 

In this case, the flowrates, concentrations and duration should be calculated separately for the periods when the 

abatement technology is or is not operating and only those that lead to actual emissions should be summed and 

reported. 

CHOICE OF EMISSION FACTORS 

Tier 3 relies on measurements of the quantities of individual materials that are released into the atmosphere and 

neither Tier 2 nor Tier 3 relies on emission factors. For Tier 1, in the absence of abatement measures, a default 

emission factor of 0.5 percent of production, not counting losses in transport and transfer of materials, is 

suggested for HFCs and PFCs, based on data supplied to AFEAS (2004). There is a wide range of substances 

that may potentially be released. However, the AFEAS data showed that the components that were lost during 

production of a particular fluorochemical had, in general, radiative forcing properties similar to those of the 

desired fluorochemical. Consequently, for sources that are not significant subcategories under key category, 

fugitive and by-product emissions are the same and are included in the 0.5 percent emission factor. 

In the case of SF6, based on German experience, a default emission factor of 0.2 percent of the total quantity of 

SF6 produced is suggested for those countries in which the predominant end use does not require highly purified 

SF6 gas (e.g., electrical equipment, insulated windows) (Preisegger, 1999). Based on experience in Japan, in 

countries where the major uses require highly purified SF6 gas (e.g., semiconductor manufacturing), the default 

value should be 8 percent because of handling losses during disposal of residual gas (i.e., the ‘heel’ that is not 

used or recycled) in returned cylinders (Suizu, 1999). If national data are available, these should be used, 

particularly for other materials not specifically listed here. 

The default emission factors are based on situations where no abatement measures are employed. If the quantity 

of gas emitted to the atmosphere is reduced by, for example, thermal oxidation of the vent stream, the quantity 

emitted should be adjusted to account for the destruction efficiency of the oxidiser and the length of time that it 

is in service. Based on the experience in the destruction of HFC-23, a default destruction efficiency of 100 

percent is suggested but the on-line time of the destruction process will have a greater effect on emissions and 

should be recorded. 
Chapter 3: Chemical Industry Emissions 

2006 IPCC Guidelines for National Greenhouse Gas Inventories 3.105 

Figure 3.17 Decision tree for emissions of fluorinated greenhouse gases from production 

processes, applicable to both fugitive and by-product emissions 

Start

Are

detailed data available

on plant-specific

estimates?

Are

national activity data

available?

No

Collect national

activity data.

Sum data for each

greenhouse gas from

plants, taking account of 

abatement (Tier 3).

Estimate emissions from 

fluorochemical plants 

adjusting for abatement 

(Tier 1).

Box 2: Tier 1

Box 5: Tier 3

Note:

1. See Volume 1 Chapter 4, Methodological Choice and Identification of Key Categories (noting Section 4.1.2 on limited resources), for

discussion of key categories and use of decision trees.

2. Tier 2 methodology may be used at this point to establish whether or not this is a key category but, as explained in Section 3.10.2.2, this 

is the only use for Tier 2.

3. Data may be collected as a country study by a third party in order to preserve confidentiality.

Yes

Is

Fluorochemical

Production a key category, and is

this production process/gas

significant1,2?

Yes

Collect emissions 

data from plants.3

Compile a list of all

fluorochemical 

manufacturers.

No

Yes

Estimate emissions from

fluorochemical plants

(Tier 1).

Is there

abatement of

emissions?

Box 1: Tier 1

No

Yes

No

CHOICE OF ACTIVITY DATA 

Again, activity data has no role in the Tiers 3 and 2 estimates, which are based on measurements. For Tier 1, the 

activity is the annual mass of the desired fluorochemical that is produced. 

Recycling 

Recycling of used gas may be done by the producers of new gas or by other recycling firms. Emissions may 

occur during handling and purification of old gas and handling of recycled gas. Specific emission factors are not 

available. Thus, good practice is to use the same default factor as for new production. 
Volume 3: Industrial Processes and Product Use 

3.106 2006 IPCC Guidelines for National Greenhouse Gas Inventories 

COMPLETENESS 

For some inventory compilers, identifying smaller producers and, in particular, recycling firms may be a difficult 

task. However, initial estimates based on the national mass balance of these fluorinated greenhouse gases should 

identify if production related emissions from such entities provide a sizeable contribution to total national 

emissions. 

DEVELOPING A CONSISTENT TIME SERIES 

Both by-product and fugitive emissions of fluorocompounds from production processes should be estimated 

using the same method for the entire time series and appropriate emission factors. If data for any years in the 

time series are unavailable for the Tier 3 method, these gaps should be filled according to the guidance provided 

in Volume 1, Chapter 5. 

3.10.2.3 UNCERTAINTY ASSESSMENT

For Tier 1, the uncertainty in activity data needs to be determined for the reporting country and statistically 

combined with the uncertainty in the default emission factor. Typically, in a well operated facility, the default 

uncertainty in activity data should be in the region of 1 percent, assuming that rigorous accounting records are 

maintained and that production is monitored by weight. The actual emission factor may range from well in 

excess of the default value to zero. The default uncertainty of the default emission factors is therefore set at 100 

percent, for example 0.5±0.5 (%). 

For Tier 3 emissions, the uncertainty of the measurements should be determined individually and combined 

(using standard statistical methods) to provide a total uncertainty for the estimate. The methodology is identical 

to that described for HFC-23 from HCFC-22. In the Tier 2 methodology, the uncertainty both of the 

measurements of efficiencies and the assignment of losses to individual compounds should be assessed. Because 

these are liable to produce a much larger uncertainty than that from Tier 3, the utility of Tier 2 is likely to be 

limited to assessing whether or not by-product fluorochemical emissions are a significant subcategory under key 

category. 

3.10.2.4 QUALITY ASSURANCE/QUALITY CONTROL (QA/QC),

REPORTING AND DOCUMENTATION

QUALITY ASSURANCE/QUALITY CONTROL 

It is good practice to conduct quality control checks as outlined in Volume 1, Chapter 6, and an expert review of 

the emissions estimates. Additional quality control checks as outlined in Volume 1, Chapter 6, quality assurance 

procedures may also be applicable, particularly if higher tier methods are used to determine emissions from this 

source category. Inventory compilers are encouraged to use higher tier QA/QC for key categories as identified in 

Volume 1, Chapter 4. 

Comparison of emissions estimates using different approaches 

Inventory compilers should compare the estimate based on aggregated producer-level data to an estimate based 

on national production data and the suggested default emission factors. They should investigate significant 

discrepancies in cooperation with the producers to determine if there are unexplained differences. 

REPORTING AND DOCUMENTATION 

Confidentiality issues may arise where there are limited numbers of manufacturers. In these cases more 

aggregate reporting of total national emissions may be necessary. If survey responses cannot be released as 

public information, third-party review of survey data may be necessary to support data verification efforts. 

It is good practice to document and archive all information required to produce the national emissions inventory 

estimates as outlined in Volume 1, Section 6.11. It is not practical to include all documentation in the national 

inventory report. However, the inventory should include summaries of methods used and references to source 

data such that the reported emissions estimates are transparent and steps in their calculation may be retraced. 
Chapter 3: Chemical Industry Emissions 

2006 IPCC Guidelines for National Greenhouse Gas Inventories 3.107 

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